### Construct a Pin

Source: https://docs.rs/indymilter/0.3.0/indymilter/type.CallbackFuture.html

Example of creating a Pin for an Unpin type.

```rust
use std::pin::Pin;

let mut val: u8 = 5;

// Since `val` doesn't care about being moved, we can safely create a "facade" `Pin`
// which will allow `val` to participate in `Pin`-bound apis  without checking that
// pinning guarantees are actually upheld.
let mut pinned: Pin<&mut u8> = Pin::new(&mut val);
```

--------------------------------

### Basic Milter Implementation

Source: https://docs.rs/indymilter/0.3.0/indymilter/fn.run.html

A minimal example demonstrating how to initialize and run a no-op milter using a TCP listener.

```rust
use indymilter::Callbacks;
use std::future;
use tokio::net::TcpListener;

let listener = TcpListener::bind("127.0.0.1:3000").await?;
let callbacks = Callbacks::<()>::new();
let config = Default::default();
let shutdown = future::pending::<()>();

indymilter::run(listener, callbacks, config, shutdown).await
```

--------------------------------

### Configuring NegotiateContext Fields

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.NegotiateContext.html?search=std%3A%3Avec

Examples for modifying the requested actions, protocol options, and macros within the context.

```rust
context.requested_actions |= Actions::ADD_RCPT | Actions::ADD_RCPT_EXT;
```

```rust
context.requested_opts |= ProtoOpts::SKIP;
```

```rust
let macros = CString::new("{auth_authen} {auth_type}").unwrap();
context.requested_macros.insert(MacroStage::Mail, macros);
```

--------------------------------

### Unwrap a Pin

Source: https://docs.rs/indymilter/0.3.0/indymilter/type.CallbackFuture.html

Example of unwrapping a Pin to retrieve the underlying pointer.

```rust
use std::pin::Pin;

let mut val: u8 = 5;
let pinned: Pin<&mut u8> = Pin::new(&mut val);

// Unwrap the pin to get the underlying mutable reference to the value. We can do
// this because `val` doesn't care about being moved, so the `Pin` was just
// a "facade" anyway.
let r = Pin::into_inner(pinned);
assert_eq!(*r, 5);
```

--------------------------------

### pub fn get(&self, name: &CStr) -> Option<&CStr>

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Macros.html

Retrieves the value associated with a specific macro name. Single-character macros can be looked up with or without braces.

```APIDOC
## pub fn get(&self, name: &CStr) -> Option<&CStr>

### Description
Returns the value associated with the given macro name, if any. Single-character macros like `i` or `{i}` can be looked up in either form (both names `i` and `{i}` return the same result).

### Parameters
- **name** (&CStr) - Required - The name of the macro to retrieve.
```

--------------------------------

### Callback Registration Methods

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Callbacks.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

Methods to configure callbacks for specific milter stages.

```APIDOC
## Callback Registration

### Methods
- **on_negotiate**: Configures the callback for the `negotiate` stage.
- **on_connect**: Configures the callback for the `connect` stage.
- **on_helo**: Configures the callback for the `helo` stage.
- **on_mail**: Configures the callback for the `mail` stage.
- **on_rcpt**: Configures the callback for the `rcpt` stage.
- **on_data**: Configures the callback for the `data` stage.
- **on_header**: Configures the callback for the `header` stage.
- **on_eoh**: Configures the callback for the `eoh` stage.
- **on_body**: Configures the callback for the `body` stage.
- **on_eom**: Configures the callback for the `eom` stage.
- **on_abort**: Configures the callback for the `abort` stage.
- **on_close**: Configures the callback for the `close` stage.
- **on_unknown**: Configures the callback for the `unknown` stage.
```

--------------------------------

### Callbacks::new

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Callbacks.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

Creates a new, empty collection of milter callbacks.

```APIDOC
## pub fn new() -> Self

### Description
Returns a new, empty collection of callbacks.
```

--------------------------------

### Callbacks<T> Methods

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Callbacks.html?search=

Methods for initializing and configuring event callbacks for the milter lifecycle.

```APIDOC
## pub fn new() -> Self

### Description
Returns a new, empty collection of callbacks.

## pub fn on_negotiate(self, callback: impl Fn(&mut NegotiateContext<T>, Actions, ProtoOpts) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `negotiate` stage.

## pub fn on_connect(self, callback: impl Fn(&mut Context<T>, CString, SocketInfo) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `connect` stage.

## pub fn on_helo(self, callback: impl Fn(&mut Context<T>, CString) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `helo` stage.

## pub fn on_mail(self, callback: impl Fn(&mut Context<T>, Vec<CString>) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `mail` stage.

## pub fn on_rcpt(self, callback: impl Fn(&mut Context<T>, Vec<CString>) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `rcpt` stage.

## pub fn on_data(self, callback: impl Fn(&mut Context<T>) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `data` stage.

## pub fn on_header(self, callback: impl Fn(&mut Context<T>, CString, CString) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `header` stage.

## pub fn on_eoh(self, callback: impl Fn(&mut Context<T>) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `eoh` stage.

## pub fn on_body(self, callback: impl Fn(&mut Context<T>, Bytes) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `body` stage.

## pub fn on_eom(self, callback: impl Fn(&mut EomContext<T>) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `eom` stage.

## pub fn on_abort(self, callback: impl Fn(&mut Context<T>) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `abort` stage.

## pub fn on_close(self, callback: impl Fn(&mut Context<T>) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `close` stage.

## pub fn on_unknown(self, callback: impl Fn(&mut Context<T>, CString) -> CallbackFuture<'_> + Send + Sync + 'static) -> Self

### Description
Configures the callback for the `unknown` stage.
```

--------------------------------

### pub async fn run<T>

Source: https://docs.rs/indymilter/0.3.0/indymilter/fn.run.html

Runs a milter that handles MTA connections until the provided shutdown future completes.

```APIDOC
## Function: run<T>

### Description
Runs a milter that handles MTA connections until it is shut down. While the future returned by `run` is awaited, it perpetually accepts new MTA connections and spawns a session task for each connection.

### Signature
`pub async fn run<T>(listener: impl Listener, callbacks: Callbacks<T>, config: Config, shutdown: impl Future) -> Result<()>`

### Parameters
- **listener** (impl Listener) - The listener to accept MTA connections.
- **callbacks** (Callbacks<T>) - The callbacks to handle milter events.
- **config** (Config) - Configuration for the milter.
- **shutdown** (impl Future) - A future that, when completed, triggers a graceful shutdown of the milter.

### Termination
For graceful termination, the milter task should be shut down by letting the `shutdown` future complete. When the `shutdown` future completes, all sessions exit cleanly as soon as possible.

### Errors
Returns an error when the listener fails to accept any new connections.
```

--------------------------------

### ContextActions Methods

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.ContextActions.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

A collection of methods for performing milter actions. Each method corresponds to specific MTA capabilities and requires corresponding flags to be enabled.

```APIDOC
## add_header(name, value)
Adds a header to the message. Requires `Actions::ADD_HEADER`.

## insert_header(index, name, value)
Inserts a header at the specified index. Requires `Actions::ADD_HEADER`.

## change_header(name, index, value)
Replaces or deletes the header at the given index. Requires `Actions::CHANGE_HEADER`.

## change_sender(mail, args)
Replaces the envelope sender, with optional ESMTP arguments. Requires `Actions::CHANGE_SENDER`.

## add_recipient(rcpt)
Adds an envelope recipient. Requires `Actions::ADD_RCPT`.

## add_recipient_ext(rcpt, args)
Adds an envelope recipient with ESMTP arguments. Requires `Actions::ADD_RCPT_EXT`.

## delete_recipient(rcpt)
Removes an envelope recipient. Requires `Actions::DELETE_RCPT`.

## replace_body(chunk)
Replaces the message body. Requires `Actions::REPLACE_BODY`.

## progress()
Reports operation-in-progress to the MTA.

## quarantine(reason)
Quarantines the message. Requires `Actions::QUARANTINE`.
```

--------------------------------

### pub fn to_hash_map(&self) -> HashMap<CString, CString>

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Macros.html

Exports all currently defined macros into a new HashMap.

```APIDOC
## pub fn to_hash_map(&self) -> HashMap<CString, CString>

### Description
Returns a new hash map containing all defined macros.
```

--------------------------------

### MacroStage::all

Source: https://docs.rs/indymilter/0.3.0/indymilter/enum.MacroStage.html?search=

Returns an iterator of all available macro stages.

```APIDOC
## pub fn all() -> impl DoubleEndedIterator<Item = Self>

### Description
Returns an iterator of all macro stages.

### Returns
- **Iterator** (impl DoubleEndedIterator<Item = Self>) - An iterator over all variants of the MacroStage enum.
```

--------------------------------

### Pinning closure captures with the pin! macro

Source: https://docs.rs/indymilter/0.3.0/indymilter/type.CallbackFuture.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

Shows the recommended approach for pinning closure captures using the pin! macro to avoid pinning contract violations.

```rust
use std::pin::pin;
use std::task::Context;
use std::future::Future;

fn move_pinned_closure(mut x: impl Future, cx: &mut Context<'_>) {
    let mut x = pin!(x);
    // Create a closure that captures `x: Pin<&mut _>`, which is safe to move.
    let mut closure = move || {
        let _ignore = x.as_mut().poll(cx);
    };
    // Call the closure, so the future can assume it has been pinned.
    closure();
    // Move the closure somewhere else.
    let mut moved = closure;
    // Calling it again here is fine (except that we might be polled a future that already
    // returned `Poll::Ready`, but that is a separate problem).
    moved();
}
```

--------------------------------

### Message::new

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/struct.Message.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

Creates a new milter protocol message instance.

```APIDOC
## Message::new

### Description
Creates a new message with the given kind and payload buffer.

### Signature
`pub fn new(kind: impl Into<u8>, buffer: impl Into<Bytes>) -> Self`

### Parameters
- **kind** (impl Into<u8>) - The message kind.
- **buffer** (impl Into<Bytes>) - The message payload buffer.
```

--------------------------------

### Export macros to HashMap

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Macros.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

Convert all currently defined macros into a HashMap of CString keys and values.

```rust
pub fn to_hash_map(&self) -> HashMap<CString, CString>
```

--------------------------------

### Reborrowing Pin with as_mut

Source: https://docs.rs/indymilter/0.3.0/indymilter/type.CallbackFuture.html

Shows how to use as_mut to reborrow a Pin<&mut Self> when calling methods that consume the pin.

```rust
use std::pin::Pin;

impl Type {
    fn method(self: Pin<&mut Self>) {
        // do something
    }

    fn call_method_twice(mut self: Pin<&mut Self>) {
        // `method` consumes `self`, so reborrow the `Pin<&mut Self>` via `as_mut`.
        self.as_mut().method();
        self.as_mut().method();
    }
}
```

--------------------------------

### ProtoOpts Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.ProtoOpts.html

The definition of the ProtoOpts struct.

```rust
pub struct ProtoOpts(/* private fields */);
```

--------------------------------

### Create New Message

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/struct.Message.html?search=u32+-%3E+bool

Constructor for creating a new Message instance.

```rust
pub fn new(kind: impl Into<u8>, buffer: impl Into<Bytes>) -> Self
```

--------------------------------

### Request protocol options

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.NegotiateContext.html

Update the requested protocol options for the MTA within the negotiate context.

```rust
context.requested_opts |= ProtoOpts::SKIP;
```

--------------------------------

### OptNegPayload Struct Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/command/struct.OptNegPayload.html

The structure definition for OptNegPayload, containing version, actions, and protocol options.

```rust
pub struct OptNegPayload {
    pub version: Version,
    pub actions: Actions,
    pub opts: ProtoOpts,
}
```

--------------------------------

### Request MTA macros

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.NegotiateContext.html

Insert requested macros into the negotiate context for a specific mail stage.

```rust
let macros = CString::new("{auth_authen} {auth_type}").unwrap();
context.requested_macros.insert(MacroStage::Mail, macros);
```

--------------------------------

### pub async fn write<S>(stream: &mut S, msg: Message) -> Result<()>

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/fn.write.html

Writes a milter protocol message to a stream. The stream must implement AsyncWrite and Unpin.

```APIDOC
## write

### Description
Writes a milter protocol message to a stream.

### Signature
`pub async fn write<S>(stream: &mut S, msg: Message) -> Result<()>`

### Constraints
- **S**: Must implement `AsyncWrite` and `Unpin` traits.
```

--------------------------------

### Pinning closure captures safely

Source: https://docs.rs/indymilter/0.3.0/indymilter/type.CallbackFuture.html

Demonstrates the risks of using Pin::new_unchecked in closures and the recommended approach using the pin! macro.

```rust
use std::pin::Pin;
use std::task::Context;
use std::future::Future;

fn move_pinned_closure(mut x: impl Future, cx: &mut Context<'_>) {
    // Create a closure that moves `x`, and then internally uses it in a pinned way.
    let mut closure = move || unsafe {
        let _ignore = Pin::new_unchecked(&mut x).poll(cx);
    };
    // Call the closure, so the future can assume it has been pinned.
    closure();
    // Move the closure somewhere else. This also moves `x`!
    let mut moved = closure;
    // Calling it again means we polled the future from two different locations,
    // violating the pinning API contract.
    moved(); // Potential UB ⚠️
}
```

```rust
use std::pin::pin;
use std::task::Context;
use std::future::Future;

fn move_pinned_closure(mut x: impl Future, cx: &mut Context<'_>) {
    let mut x = pin!(x);
    // Create a closure that captures `x: Pin<&mut _>`, which is safe to move.
    let mut closure = move || {
        let _ignore = x.as_mut().poll(cx);
    };
    // Call the closure, so the future can assume it has been pinned.
    closure();
    // Move the closure somewhere else.
    let mut moved = closure;
    // Calling it again here is fine (except that we might be polled a future that already
    // returned `Poll::Ready`, but that is a separate problem).
    moved();
}
```

--------------------------------

### Request MTA actions

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.NegotiateContext.html

Update the requested actions for the MTA within the negotiate context.

```rust
context.requested_actions |= Actions::ADD_RCPT | Actions::ADD_RCPT_EXT;
```

--------------------------------

### ProtoOpts constants

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.ProtoOpts.html?search=std%3A%3Avec

Constants used to configure milter protocol options, such as skipping stages or setting noreply behavior.

```rust
pub const NO_CONNECT: Self
```

```rust
pub const NO_HELO: Self
```

```rust
pub const NO_MAIL: Self
```

```rust
pub const NO_RCPT: Self
```

```rust
pub const NO_DATA: Self
```

```rust
pub const NO_HEADER: Self
```

```rust
pub const NO_EOH: Self
```

```rust
pub const NO_BODY: Self
```

```rust
pub const NO_UNKNOWN: Self
```

```rust
pub const NOREPLY_CONNECT: Self
```

```rust
pub const NOREPLY_HELO: Self
```

```rust
pub const NOREPLY_MAIL: Self
```

```rust
pub const NOREPLY_RCPT: Self
```

```rust
pub const NOREPLY_DATA: Self
```

```rust
pub const NOREPLY_HEADER: Self
```

```rust
pub const NOREPLY_EOH: Self
```

```rust
pub const NOREPLY_BODY: Self
```

```rust
pub const NOREPLY_UNKNOWN: Self
```

```rust
pub const REJECTED_RCPT: Self
```

```rust
pub const LEADING_SPACE: Self
```

```rust
pub const SKIP: Self
```

--------------------------------

### Config Struct Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Config.html

The primary structure used for milter configuration.

```rust
pub struct Config {
    pub max_connections: usize,
    pub actions: Actions,
    pub connection_timeout: Duration,
}
```

--------------------------------

### run

Source: https://docs.rs/indymilter/0.3.0/indymilter/index.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

The run function is the main entry point to the indymilter API. It executes a milter that handles MTA connections until it is shut down.

```APIDOC
## run

### Description
Runs a milter that handles MTA connections until it is shut down. This function returns a future that can be awaited.

### Signature
`pub async fn run<L, C>(listener: L, config: Config, callbacks: C) -> Result<(), Box<dyn Error>>`

### Parameters
- **listener** (L) - The listener implementation (e.g., a Tokio-based listener).
- **config** (Config) - The milter configuration settings.
- **callbacks** (C) - The callback closures defined for each milter stage.
```

--------------------------------

### run

Source: https://docs.rs/indymilter/0.3.0/indymilter/index.html?search=

The run function is the main entry point to the indymilter API. It executes a milter that handles MTA connections until it is shut down.

```APIDOC
## run

### Description
Runs a milter that handles MTA connections until it is shut down. This function returns a future that can be awaited to execute the milter application.

### Signature
`pub async fn run<L, C>(listener: L, config: Config, callbacks: C) -> Result<(), Error>`

### Parameters
- **listener** (L) - Required - A listener implementing the Listener trait.
- **config** (Config) - Required - The milter configuration.
- **callbacks** (C) - Required - The callback closures for each milter stage.
```

--------------------------------

### pub async fn read<S>(stream: &mut S) -> Result<Message>

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/fn.read.html

Reads a milter protocol message from a stream.

```APIDOC
## pub async fn read<S>(stream: &mut S) -> Result<Message>

### Description
Reads a milter protocol message from a stream.

### Signature
`pub async fn read<S>(stream: &mut S) -> Result<Message> where S: AsyncRead + Unpin`

### Parameters
- **stream** (&mut S) - Required - An asynchronous stream that implements AsyncRead and Unpin traits.

### Returns
- **Result<Message>** - Returns a Result containing the parsed Message if successful, or an error if the read operation fails.
```

--------------------------------

### Command Parsing and Conversion

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/command/enum.Command.html?search=

Methods for parsing a command from a message and converting a command back into a message.

```rust
pub fn parse_command(msg: Message) -> Result<Self, ParseCommandError>
```

```rust
pub fn into_message(self) -> Message
```

--------------------------------

### into_message

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/reply/enum.Reply.html?search=std%3A%3Avec

Converts a Reply instance into a milter protocol message.

```APIDOC
## pub fn into_message(self) -> Message

### Description
Converts this reply to a milter protocol message.

### Returns
- **Message** - The resulting milter protocol message.
```

--------------------------------

### Unsafe Pinning with Rc

Source: https://docs.rs/indymilter/0.3.0/indymilter/type.CallbackFuture.html

Demonstrates how using Pin::new_unchecked on an Rc can lead to undefined behavior due to potential aliasing and mutable access after dropping the pin.

```rust
use std::rc::Rc;
use std::pin::Pin;

fn move_pinned_rc<T>(mut x: Rc<T>) {
    // This should mean the pointee can never move again.
    let pin = unsafe { Pin::new_unchecked(Rc::clone(&x)) };
    {
        let p: Pin<&T> = pin.as_ref();
        // ...
    }
    drop(pin);

    let content = Rc::get_mut(&mut x).unwrap(); // Potential UB down the road ⚠️
    // Now, if `x` was the only reference, we have a mutable reference to
    // data that we pinned above, which we could use to move it as we have
    // seen in the previous example. We have violated the pinning API contract.
}
```

--------------------------------

### pub fn index(&self) -> i32

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/struct.TryFromIndexError.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

Retrieves the index that caused the conversion error.

```APIDOC
### pub fn index(&self) -> i32

#### Description
Returns the index that caused the conversion error.

#### Returns
- **i32** - The index value that triggered the error.
```

--------------------------------

### pub fn index(&self) -> i32

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/struct.TryFromIndexError.html?search=u32+-%3E+bool

Retrieves the index that caused the conversion error.

```APIDOC
### Method
`pub fn index(&self) -> i32`

### Description
Returns the index that caused the conversion error.

### Returns
- **i32**: The index value that triggered the error.
```

--------------------------------

### run

Source: https://docs.rs/indymilter/0.3.0/indymilter/index.html

The run function is the main entry point to the indymilter API. It returns a future that can be awaited to execute a milter application and handle MTA connections until shutdown.

```APIDOC
## run

### Description
Runs a milter that handles MTA connections until it is shut down. This function returns a future that can be awaited.

### Signature
`pub async fn run<L, C>(listener: L, config: Config, callbacks: C) -> Result<(), Box<dyn Error>>`

### Parameters
- **listener** (L) - Required - A listener implementing the Listener trait.
- **config** (Config) - Required - The milter configuration.
- **callbacks** (C) - Required - The callback closures for each milter stage.
```

--------------------------------

### Function Signature

Source: https://docs.rs/indymilter/0.3.0/indymilter/fn.run.html

The signature for the run function, requiring a listener, callbacks, configuration, and a shutdown future.

```rust
pub async fn run<T>(
    listener: impl Listener,
    callbacks: Callbacks<T>,
    config: Config,
    shutdown: impl Future,
) -> Result<()>
where
    T: Send + 'static,
```

--------------------------------

### Safe Pinning with pin! Macro

Source: https://docs.rs/indymilter/0.3.0/indymilter/type.CallbackFuture.html?search=u32+-%3E+bool

Uses the pin! macro to safely pin a future before capturing it in a closure.

```rust
use std::pin::pin;
use std::task::Context;
use std::future::Future;

fn move_pinned_closure(mut x: impl Future, cx: &mut Context<'_>) {
    let mut x = pin!(x);
    // Create a closure that captures `x: Pin<&mut _>`, which is safe to move.
    let mut closure = move || {
        let _ignore = x.as_mut().poll(cx);
    };
    // Call the closure, so the future can assume it has been pinned.
    closure();
    // Move the closure somewhere else.
    let mut moved = closure;
    // Calling it again here is fine (except that we might be polling a future that already
    // returned `Poll::Ready`, but that is a separate problem).
    moved();
}
```

--------------------------------

### IntoCString::into_c_string

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.IntoCString.html?search=u32+-%3E+bool

Converts the implementing type into a CString.

```APIDOC
## fn into_c_string(self) -> CString

### Description
Converts the value into a CString. This is an infallible conversion.

### Signature
`fn into_c_string(self) -> CString`

### Implementations
- `impl IntoCString for &CStr`
- `impl IntoCString for &str`
- `impl IntoCString for CString`
- `impl IntoCString for String`
```

--------------------------------

### indymilter::run

Source: https://docs.rs/indymilter/0.3.0/indymilter/fn.run.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

Runs a milter that handles MTA connections until it is shut down. The function accepts a listener, callbacks, configuration, and a shutdown future.

```APIDOC
## Function: indymilter::run<T>

### Description
Runs a milter that handles MTA connections until it is shut down. While the future returned by `run` is awaited, it perpetually accepts new MTA connections and spawns a session task for each connection.

### Signature
`pub async fn run<T>(listener: impl Listener, callbacks: Callbacks<T>, config: Config, shutdown: impl Future) -> Result<()>`

### Parameters
- **listener** (impl Listener) - The listener to accept MTA connections.
- **callbacks** (Callbacks<T>) - The callbacks to handle milter events.
- **config** (Config) - Configuration for the milter.
- **shutdown** (impl Future) - A future that, when completed, triggers a graceful shutdown of the milter.

### Errors
Returns an error if the listener fails to accept new connections.

### Example
```rust
use indymilter::Callbacks;
use std::future;
use tokio::net::TcpListener;

let listener = TcpListener::bind("127.0.0.1:3000").await?;
let callbacks = Callbacks::<()>::new();
let config = Default::default();
let shutdown = future::pending::<()>();

indymilter::run(listener, callbacks, config, shutdown).await
```
```

--------------------------------

### progress

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.ContextActions.html?search=std%3A%3Avec

Reports operation-in-progress to the MTA.

```APIDOC
fn progress() -> Future<Result<(), ActionError>>
```

--------------------------------

### Macros::to_hash_map

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Macros.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

Converts the collection of defined macros into a HashMap.

```APIDOC
## fn to_hash_map(&self) -> HashMap<CString, CString>

### Description
Returns a new hash map containing all currently defined macros.
```

--------------------------------

### Define NegotiateContext structure

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.NegotiateContext.html

The structure definition for NegotiateContext, which holds user data and configuration for the negotiation phase.

```rust
pub struct NegotiateContext<T: Send> {
    pub data: Option<T>,
    pub reply: SmtpReply,
    pub requested_actions: Actions,
    pub requested_opts: ProtoOpts,
    pub requested_macros: HashMap<MacroStage, CString>,
}
```

--------------------------------

### IntoCString Method Signature

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.IntoCString.html?search=u32+-%3E+bool

The required method signature for converting a value into a CString.

```rust
fn into_c_string(self) -> CString
```

--------------------------------

### Unsafe Pinning with Mutable References

Source: https://docs.rs/indymilter/0.3.0/indymilter/type.CallbackFuture.html

Demonstrates how using Pin::new_unchecked on a mutable reference can lead to undefined behavior if the value is moved after pinning.

```rust
use std::mem;
use std::pin::Pin;

fn move_pinned_ref<T>(mut a: T, mut b: T) {
    unsafe {
        let p: Pin<&mut T> = Pin::new_unchecked(&mut a);
        // This should mean the pointee `a` can never move again.
    }
    mem::swap(&mut a, &mut b); // Potential UB down the road ⚠️
    // The address of `a` changed to `b`'s stack slot, so `a` got moved even
    // though we have previously pinned it! We have violated the pinning API contract.
}
```

--------------------------------

### Overwriting pinned data with set

Source: https://docs.rs/indymilter/0.3.0/indymilter/type.CallbackFuture.html

Demonstrates using the set method to replace the value pointed to by a Pin.

```rust
use std::pin::Pin;

let mut val: u8 = 5;
let mut pinned: Pin<&mut u8> = Pin::new(&mut val);
println!("{}", pinned); // 5
pinned.set(10);
println!("{}", pinned); // 10
```

--------------------------------

### TryFromIndexError index method

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/struct.TryFromIndexError.html?search=

Retrieves the index that caused the conversion error.

```rust
pub fn index(&self) -> i32
```

--------------------------------

### pub fn byte(&self) -> u8

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/struct.TryFromByteError.html?search=std%3A%3Avec

Returns the byte that caused the conversion error.

```APIDOC
## pub fn byte(&self) -> u8

### Description
Returns the byte that caused the conversion error.

### Signature
`pub fn byte(&self) -> u8`
```

--------------------------------

### ConnInfoPayload Struct Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/command/struct.ConnInfoPayload.html

The structure definition for ConnInfoPayload, containing the hostname and socket information fields.

```rust
pub struct ConnInfoPayload {
    pub hostname: CString,
    pub socket_info: SocketInfo,
}
```

--------------------------------

### Accessing PROTOCOL_VERSION

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/constant.PROTOCOL_VERSION.html

The constant represents the Milter protocol version as a Version type.

```rust
pub const PROTOCOL_VERSION: Version = 6;
```

--------------------------------

### ContextActions Trait Methods for EomActions

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.EomActions.html

Asynchronous methods available on EomActions for performing milter operations.

```rust
fn add_header<'cx, 'k, 'v, 'async_trait>( &'cx self, name: impl 'async_trait + IntoCString + Send + 'k, value: impl 'async_trait + IntoCString + Send + 'v, ) -> Pin<Box<dyn Future<Output = Result<(), ActionError>> + Send + 'async_trait>>
where Self: 'async_trait, 'cx: 'async_trait, 'k: 'async_trait, 'v: 'async_trait,
```

```rust
fn insert_header<'cx, 'k, 'v, 'async_trait>( &'cx self, index: i32, name: impl 'async_trait + IntoCString + Send + 'k, value: impl 'async_trait + IntoCString + Send + 'v, ) -> Pin<Box<dyn Future<Output = Result<(), ActionError>> + Send + 'async_trait>>
where Self: 'async_trait, 'cx: 'async_trait, 'k: 'async_trait, 'v: 'async_trait,
```

```rust
fn change_header<'cx, 'k, 'v, 'async_trait>( &'cx self, name: impl 'async_trait + IntoCString + Send + 'k, index: i32, value: Option<impl 'async_trait + IntoCString + Send + 'v>, ) -> Pin<Box<dyn Future<Output = Result<(), ActionError>> + Send + 'async_trait>>
where Self: 'async_trait, 'cx: 'async_trait, 'k: 'async_trait, 'v: 'async_trait,
```

```rust
fn change_sender<'cx, 'a, 'b, 'async_trait>( &'cx self, mail: impl 'async_trait + IntoCString + Send + 'a, args: Option<impl 'async_trait + IntoCString + Send + 'b>, ) -> Pin<Box<dyn Future<Output = Result<(), ActionError>> + Send + 'async_trait>>
where Self: 'async_trait, 'cx: 'async_trait, 'a: 'async_trait, 'b: 'async_trait,
```

```rust
fn add_recipient<'cx, 'a, 'async_trait>( &'cx self, rcpt: impl 'async_trait + IntoCString + Send + 'a, ) -> Pin<Box<dyn Future<Output = Result<(), ActionError>> + Send + 'async_trait>>
where Self: 'async_trait, 'cx: 'async_trait, 'a: 'async_trait,
```

```rust
fn add_recipient_ext<'cx, 'a, 'b, 'async_trait>( &'cx self, rcpt: impl 'async_trait + IntoCString + Send + 'a, args: Option<impl 'async_trait + IntoCString + Send + 'b>, ) -> Pin<Box<dyn Future<Output = Result<(), ActionError>> + Send + 'async_trait>>
where Self: 'async_trait, 'cx: 'async_trait, 'a: 'async_trait, 'b: 'async_trait,
```

```rust
fn delete_recipient<'cx, 'a, 'async_trait>( &'cx self, rcpt: impl 'async_trait + IntoCString + Send + 'a, ) -> Pin<Box<dyn Future<Output = Result<(), ActionError>> + Send + 'async_trait>>
where Self: 'async_trait, 'cx: 'async_trait, 'a: 'async_trait,
```

```rust
fn replace_body<'cx, 'a, 'async_trait>( &'cx self, chunk: &'a [u8], ) -> Pin<Box<dyn Future<Output = Result<(), ActionError>> + Send + 'async_trait>>
where Self: 'async_trait, 'cx: 'async_trait, 'a: 'async_trait,
```

```rust
fn progress<'cx, 'async_trait>( &'cx self, ) -> Pin<Box<dyn Future<Output = Result<(), ActionError>> + Send + 'async_trait>>
where Self: 'async_trait, 'cx: 'async_trait,
```

```rust
fn quarantine<'cx, 'a, 'async_trait>( &'cx self, reason: impl 'async_trait + IntoCString + Send + 'a, ) -> Pin<Box<dyn Future<Output = Result<(), ActionError>> + Send + 'async_trait>>
where Self: 'async_trait, 'cx: 'async_trait, 'a: 'async_trait,
```

--------------------------------

### Configure SMTP error reply

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.SmtpReply.html?search=std%3A%3Avec

Method to set an SMTP error reply using a return code, extended code, and message.

```rust
fn set_error_reply<I, T>( &mut self, rcode: &str, xcode: Option<&str>, message: I, ) -> Result<(), SmtpReplyError>
where I: IntoIterator<Item = T>, T: IntoCString,
```

--------------------------------

### Define Version type alias

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/type.Version.html

Represents the milter protocol version as a u32.

```rust
pub type Version = u32;
```

--------------------------------

### Reply Enum Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/reply/enum.Reply.html

The complete definition of the Reply enum, including all variants and their associated fields.

```rust
pub enum Reply {
Show 18 variants    AddRcpt {
        rcpt: CString,
    },
    DeleteRcpt {
        rcpt: CString,
    },
    AddRcptExt {
        rcpt: CString,
        args: Option<CString>,
    },
    OptNeg {
        version: Version,
        actions: Actions,
        opts: ProtoOpts,
        macros: HashMap<MacroStage, CString>,
    },
    Accept,
    ReplaceBody {
        chunk: Bytes,
    },
    Continue,
    Discard,
    ChangeSender {
        mail: CString,
        args: Option<CString>,
    },
    AddHeader {
        name: CString,
        value: CString,
    },
    InsertHeader {
        index: i32,
        name: CString,
        value: CString,
    },
    ChangeHeader {
        name: CString,
        index: i32,
        value: CString,
    },
    Progress,
    Quarantine {
        reason: CString,
    },
    Reject,
    Skip,
    Tempfail,
    ReplyCode {
        reply: CString,
    },
}
```

--------------------------------

### EnvAddrPayload Struct Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/command/struct.EnvAddrPayload.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

The primary structure definition for EnvAddrPayload, containing a vector of CString arguments.

```rust
pub struct EnvAddrPayload {
    pub args: Vec<CString>,
}
```

--------------------------------

### IntoCString Implementations

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.IntoCString.html?search=u32+-%3E+bool

Implementations of the IntoCString trait for various foreign types.

```rust
impl IntoCString for &CStr
fn into_c_string(self) -> CString
```

```rust
impl IntoCString for &str
fn into_c_string(self) -> CString
```

```rust
impl IntoCString for CString
fn into_c_string(self) -> Self
```

```rust
impl IntoCString for String
fn into_c_string(self) -> CString
```

--------------------------------

### quarantine

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.ContextActions.html?search=std%3A%3Avec

Quarantines the message. Requires Actions::QUARANTINE flag.

```APIDOC
fn quarantine(reason: impl IntoCString) -> Future<Result<(), ActionError>>
```

--------------------------------

### add_header

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.ContextActions.html?search=std%3A%3Avec

Adds a header to the message. Requires Actions::ADD_HEADER flag.

```APIDOC
fn add_header(name: impl IntoCString, value: impl IntoCString) -> Future<Result<(), ActionError>>
```

--------------------------------

### Define Macros struct

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Macros.html

The definition of the Macros struct.

```rust
pub struct Macros(/* private fields */);
```

--------------------------------

### Command Enum Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/command/enum.Command.html

The Command enum lists all supported milter protocol commands as variants.

```rust
pub enum Command {
Show 15 variants    Abort,
    BodyChunk(Bytes),
    ConnInfo(ConnInfoPayload),
    DefMacros(MacroPayload),
    BodyEnd(Bytes),
    Helo(HeloPayload),
    QuitNc,
    Header(HeaderPayload),
    Mail(EnvAddrPayload),
    Eoh,
    OptNeg(OptNegPayload),
    Quit,
    Rcpt(EnvAddrPayload),
    Data,
    Unknown(UnknownPayload),
}
```

--------------------------------

### fn into_c_string(self) -> CString

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.IntoCString.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

Converts the implementing type into a CString. This method is required for all types implementing the IntoCString trait.

```APIDOC
## fn into_c_string(self) -> CString

### Description
Converts the value into a CString. This is an infallible conversion.

### Signature
`fn into_c_string(self) -> CString`

### Implementations
- `&CStr`
- `&str`
- `CString`
- `String`
```

--------------------------------

### MacroStage::all_sorted_by_index

Source: https://docs.rs/indymilter/0.3.0/indymilter/enum.MacroStage.html?search=

Returns an iterator of all macro stages, sorted by their underlying index value.

```APIDOC
## pub fn all_sorted_by_index() -> impl DoubleEndedIterator<Item = Self>

### Description
Returns an iterator of all macro stages, sorted by their index value.

### Returns
- **Iterator** (impl DoubleEndedIterator<Item = Self>) - An iterator over all variants of the MacroStage enum, ordered by index.
```

--------------------------------

### Macros::get

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Macros.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

Retrieves the value associated with a specific macro name. Single-character macros can be looked up with or without braces.

```APIDOC
## fn get(&self, name: &CStr) -> Option<&CStr>

### Description
Returns the value associated with the given macro name, if any. Single-character macros like `i` or `{i}` can be looked up in either form.

### Parameters
- **name** (&CStr) - Required - The name of the macro to retrieve.
```

--------------------------------

### HeaderPayload Struct Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/command/struct.HeaderPayload.html?search=

The primary structure definition for HeaderPayload.

```rust
pub struct HeaderPayload {
    pub name: CString,
    pub value: CString,
}
```

--------------------------------

### MacroPayload Struct Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/command/struct.MacroPayload.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

The structure definition for MacroPayload, containing the stage and macros fields.

```rust
pub struct MacroPayload {
    pub stage: MacroStage,
    pub macros: Vec<CString>,
}
```

--------------------------------

### add_recipient_ext

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.ContextActions.html?search=std%3A%3Avec

Adds an envelope recipient with ESMTP arguments. Requires Actions::ADD_RCPT_EXT flag.

```APIDOC
fn add_recipient_ext(rcpt: impl IntoCString, args: Option<impl IntoCString>) -> Future<Result<(), ActionError>>
```

--------------------------------

### replace_body

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.ContextActions.html?search=std%3A%3Avec

Replaces the message body. Requires Actions::REPLACE_BODY flag.

```APIDOC
fn replace_body(chunk: &[u8]) -> Future<Result<(), ActionError>>
```

--------------------------------

### byte()

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/struct.TryFromByteError.html

Retrieves the byte that caused the conversion error.

```APIDOC
## pub fn byte(&self) -> u8

### Description
Returns the byte that caused the conversion error.

### Returns
- **u8** - The byte value that triggered the error.
```

--------------------------------

### parse_reply

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/reply/enum.Reply.html?search=std%3A%3Avec

Parses a milter protocol message into a Reply instance.

```APIDOC
## pub fn parse_reply(msg: Message) -> Result<Self, ParseReplyError>

### Description
Parses a reply from a milter protocol message.

### Parameters
- **msg** (Message) - Required - The milter protocol message to parse.

### Returns
- **Result<Self, ParseReplyError>** - Returns the parsed Reply instance or a ParseReplyError if parsing fails.
```

--------------------------------

### change_header

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.ContextActions.html?search=std%3A%3Avec

Replaces or deletes a header at a specific index. Requires Actions::CHANGE_HEADER flag.

```APIDOC
fn change_header(name: impl IntoCString, index: i32, value: Option<impl IntoCString>) -> Future<Result<(), ActionError>>
```

--------------------------------

### Context Struct Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Context.html

The primary structure used to manage state and responses within an indymilter callback.

```rust
pub struct Context<T: Send> {
    pub data: Option<T>,
    pub macros: Macros,
    pub reply: SmtpReply,
}
```

--------------------------------

### set_error_reply

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.SmtpReply.html

Configures an SMTP error reply for the current SmtpReply instance.

```APIDOC
## fn set_error_reply<I, T>(&mut self, rcode: &str, xcode: Option<&str>, message: I) -> Result<(), SmtpReplyError>

### Description
Configures an SMTP error reply. This method allows setting the SMTP return code, extended status code, and the associated message.

### Parameters
- **rcode** (&str) - Required - The SMTP return code (e.g., "550").
- **xcode** (Option<&str>) - Required - The optional extended status code (e.g., "5.7.1").
- **message** (I) - Required - An iterator of messages to be sent as part of the reply.

### Returns
- **Result<(), SmtpReplyError>** - Returns Ok(()) on success, or an SmtpReplyError if the configuration fails.
```

--------------------------------

### Actions struct definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Actions.html

The primary structure representing eom action flags.

```rust
pub struct Actions(/* private fields */);
```

--------------------------------

### insert_header

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.ContextActions.html?search=std%3A%3Avec

Inserts a header at a specific index. Requires Actions::ADD_HEADER flag.

```APIDOC
fn insert_header(index: i32, name: impl IntoCString, value: impl IntoCString) -> Future<Result<(), ActionError>>
```

--------------------------------

### Unsafe Pinning in Closures

Source: https://docs.rs/indymilter/0.3.0/indymilter/type.CallbackFuture.html?search=u32+-%3E+bool

Demonstrates the potential for undefined behavior when using Pin::new_unchecked on moved closure captures.

```rust
use std::pin::Pin;
use std::task::Context;
use std::future::Future;

fn move_pinned_closure(mut x: impl Future, cx: &mut Context<'_>) {
    // Create a closure that moves `x`, and then internally uses it in a pinned way.
    let mut closure = move || unsafe {
        let _ignore = Pin::new_unchecked(&mut x).poll(cx);
    };
    // Call the closure, so the future can assume it has been pinned.
    closure();
    // Move the closure somewhere else. This also moves `x`!
    let mut moved = closure;
    // Calling it again means we polled the future from two different locations,
    // violating the pinning API contract.
    moved(); // Potential UB ⚠️
}
```

--------------------------------

### UnknownPayload Struct Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/command/struct.UnknownPayload.html

The structure definition for UnknownPayload, which holds a CString argument.

```rust
pub struct UnknownPayload {
    pub arg: CString,
}
```

--------------------------------

### Define TryFromByteError struct

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/struct.TryFromByteError.html?search=

The definition of the TryFromByteError struct with private fields.

```rust
pub struct TryFromByteError(/* private fields */);
```

--------------------------------

### IntoCString Trait Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.IntoCString.html

The core trait definition requiring the implementation of the into_c_string method.

```rust
pub trait IntoCString {
    // Required method
    fn into_c_string(self) -> CString;
}
```

--------------------------------

### Define the Listener trait

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.Listener.html

The core trait definition requiring an asynchronous I/O type and a poll_accept method.

```rust
pub trait Listener {
    type Io: AsyncRead + AsyncWrite + Unpin + Send + 'static;

    // Required method
    fn poll_accept(&mut self, cx: &mut Context<'_>) -> Poll<Result<Self::Io>>;

    // Provided method
    fn accept(&mut self) -> ListenerAcceptFut<'_, Self>
       where Self: Sized { ... }
}
```

--------------------------------

### ReplyKind Enum Definition

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/reply/enum.ReplyKind.html?search=

The enumeration of all possible reply kinds supported by the milter protocol.

```rust
pub enum ReplyKind {
Show 18 variants    AddRcpt,
    DeleteRcpt,
    AddRcptExt,
    OptNeg,
    Accept,
    ReplaceBody,
    Continue,
    Discard,
    ChangeSender,
    AddHeader,
    InsertHeader,
    ChangeHeader,
    Progress,
    Quarantine,
    Reject,
    Skip,
    Tempfail,
    ReplyCode,
}
```

--------------------------------

### change_sender

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.ContextActions.html

Replaces the envelope sender. Requires the Actions::CHANGE_SENDER flag.

```APIDOC
## change_sender(mail, args)

### Description
Replaces the envelope sender, with optional ESMTP arguments. This operation must be enabled with the `Actions::CHANGE_SENDER` flag.

### Parameters
- **mail** (impl IntoCString) - The new sender address.
- **args** (Option<impl IntoCString>) - Optional ESMTP arguments.

### Returns
- **Result<(), ActionError>** - Returns an empty result on success or an ActionError on failure.
```

--------------------------------

### Write milter message signature

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/fn.write.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

The function requires a mutable reference to an AsyncWrite stream and a Message object.

```rust
pub async fn write<S>(stream: &mut S, msg: Message) -> Result<()> 
where 
    S: AsyncWrite + Unpin,
```

--------------------------------

### Write milter message to stream

Source: https://docs.rs/indymilter/0.3.0/indymilter/message/fn.write.html

Writes a milter protocol message to an asynchronous stream that implements AsyncWrite and Unpin.

```rust
pub async fn write<S>(stream: &mut S, msg: Message) -> Result<()>
where
    S: AsyncWrite + Unpin,
```

--------------------------------

### Define SmtpReply struct

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.SmtpReply.html?search=

The definition of the SmtpReply struct with private fields.

```rust
pub struct SmtpReply { /* private fields */ }
```

--------------------------------

### change_sender

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.ContextActions.html?search=std%3A%3Avec

Replaces the envelope sender with optional ESMTP arguments. Requires Actions::CHANGE_SENDER flag.

```APIDOC
fn change_sender(mail: impl IntoCString, args: Option<impl IntoCString>) -> Future<Result<(), ActionError>>
```

--------------------------------

### add_recipient

Source: https://docs.rs/indymilter/0.3.0/indymilter/trait.ContextActions.html?search=std%3A%3Avec

Adds an envelope recipient. Requires Actions::ADD_RCPT flag.

```APIDOC
fn add_recipient(rcpt: impl IntoCString) -> Future<Result<(), ActionError>>
```

--------------------------------

### Retrieve macro value

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.Macros.html?search=Option%3CT%3E%2C+%28T+-%3E+U%29+-%3E+Option%3CU%3E

Look up a macro value by name. Single-character macros can be queried with or without curly braces.

```rust
pub fn get(&self, name: &CStr) -> Option<&CStr>
```

--------------------------------

### set_error_reply

Source: https://docs.rs/indymilter/0.3.0/indymilter/struct.SmtpReply.html?search=std%3A%3Avec

Configures an SMTP error reply for the current transaction.

```APIDOC
## fn set_error_reply<I, T>(&mut self, rcode: &str, xcode: Option<&str>, message: I) -> Result<(), SmtpReplyError>

### Description
Configures an SMTP error reply. This method allows setting the SMTP return code, an optional extended SMTP code, and a message body.

### Parameters
- **rcode** (&str) - Required - The SMTP return code (e.g., "550").
- **xcode** (Option<&str>) - Required - The optional extended SMTP status code (e.g., "5.7.1").
- **message** (I) - Required - The error message, which must implement IntoIterator where items implement IntoCString.

### Returns
- **Result<(), SmtpReplyError>** - Returns Ok(()) on success, or an SmtpReplyError if the configuration fails.
```