Crate smtpd 

smtpd

smtpd is an asynchronous, extensible SMTP server library built on top of tokio. Inspired by smtpd. It provides flexible support for authentication, TLS, and custom handling of SMTP commands.

Features

• Asynchronous SMTP server using Tokio.
• Supports authentication mechanisms: AuthMach::Plain, AuthMach::Login, AuthMach::CramMD5.
• TLS support (STARTTLS and implicit TLS) with optional native-tls (feature native-tls-backend) or rustls (feature rustls-backend) backend.
• Customizable handlers for AUTH, RCPT, and DATA commands via the Handler struct’s SmtpHandler::handle_auth, SmtpHandler::handle_email, and SmtpHandler::handle_rcpt method
• Configurable limits for message size and recipients.

Example

use smtpd::{async_trait, start_server, SmtpConfig, AuthMach};

#[tokio::main]
async fn main() -> Result<(), std::io::Error> {
    let config = SmtpConfig {
        bind_addr: "127.0.0.1:2525".to_string(),
        require_auth: true,
        auth_machs: vec![AuthMach::Plain, AuthMach::Login],
        ..Default::default()
    };

    let factory = MyHandlerFactory {};

    start_server(config, factory).await?;
    Ok(())
}

struct MyHandler {}

#[async_trait]
impl smtpd::SmtpHandler for MyHandler {
    async fn handle_auth(
        &mut self,
        _session: &smtpd::Session,
        data: smtpd::AuthData,
    ) -> Result<smtpd::Response, smtpd::Error> {
        let (username, password, _) = data.data();

        if username == "abc" && password == "efg" {
            return Ok(smtpd::Response::Default);
        }

        Err(smtpd::Error::Abort)
    }

    async fn handle_rcpt(
        &mut self,
        _session: &smtpd::Session,
        to: &str,
    ) -> Result<smtpd::Response, smtpd::Error> {
        // allow recipients only from gmail
        if to.ends_with("gmail.com") {
            return Ok(smtpd::Response::Default);
        }

        Err(smtpd::Error::Abort)
    }
}

struct MyHandlerFactory;

impl smtpd::SmtpHandlerFactory for MyHandlerFactory {
    type Handler = MyHandler;

    fn new_handler(&self, _session: &smtpd::Session) -> Self::Handler {
        MyHandler {}
    }
}

Modules

• session: Represents a client session.
• handler: Defines traits for handling SMTP commands.
• tls: TLS configuration and provider utilities.
• stream: Connection stream abstraction with read/write helpers.
• utils: Parsing and helper functions for SMTP commands.

Structs

Session

Represents an active SMTP session.

SmtpConfig

SMTP Server Configuration

SmtpServer

The core SMTP server struct.

Enums

AuthData

Represents the parsed authentication data provided by the client.

AuthMach

Represents the supported SMTP authentication mechanisms.

Error

Error for handler operations.

Response

Represents an SMTP response that can be written to the client stream.

TlsConfig

Represents the TLS configuration for the SMTP server.

TlsMode

Specifies the TLS mode for the SMTP server.

Traits

SmtpHandler

Defines the async hook interface for handling key SMTP events: authentication (AUTH), recipient validation (RCPT TO), and message delivery (DATA).

SmtpHandlerFactory

Defines how new SmtpHandler instances are created per session.

Functions

start_server

Starts an SMTP server with the provided configuration and handler factory.

Type Aliases

Result

Convenient alias for handler results

Attribute Macros

async_trait