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smtp_send

SMTP email sending library with DKIM signing, MX lookup, and automatic bounce handling.

Features

• DKIM Signing: RSA-SHA256 with RFC 6376 header protection (N+1 signing)
• MX Lookup: DNS-over-QUIC via idot
• Concurrent Sending: Parallel delivery grouped by domain
• Failover: Tries multiple MX servers on failure
• Bounce Handling: Auto-generates RFC 5321 compliant rejection reports
• Loop Prevention: Checks Received header count (max 30) and Auto-Submitted/Return-Path headers
• DKIM Cache: 600s TTL cache for signers

Usage

use smtp_send::Send;
use mail_struct::Mail;

#[tokio::main]
async fn main() {
    // Load DKIM private key
    let sk = std::fs::read("private.key").unwrap();
    
    // Create sender with DKIM selector
    let sender = Send::new("default", &sk);
    
    // Build email
    let mut mail = Mail::new(
        "sender@example.com",
        ["recipient@example.com"],
        b"Subject: Test\r\n\r\nHello".to_vec(),
    ).unwrap();
    
    // Send email
    let result = sender.send(&mut mail).await;
    
    println!("sent: {}, errors: {}", result.success, result.error_li.len());
}

API

Send

pub struct Send {
    pub selector: String,  // DKIM selector
    pub sk: Sk,            // DKIM private key
}

impl Send {
    // Create sender
    fn new(selector: impl Into<String>, sk: impl AsRef<[u8]>) -> Self;
    
    // Send email with Received header and DKIM signing
    async fn send(&self, mail: &mut Mail) -> SendResult;
}

SendResult

pub struct SendResult {
    pub success: usize,        // Number of successful deliveries
    pub error_li: Vec<Error>,  // List of errors
}

Error

Standalone Functions

// Send without Received header (for direct sending)
pub async fn send(mail: &Mail, signer: Option<&Signer>) -> SendResult;

// Create DKIM signer (cached), returns None on failure
pub fn signer(selector: &str, host: &str, sk: &Sk) -> Option<RefVal<String, Signer>>;

// Check if Received headers exceed limit
pub fn recv_overflow(body: &[u8]) -> bool;

// Add Received header
pub fn add_received(body: &mut Vec<u8>, from: &str, by: &str);

pub const MAX_RECEIVED: usize = 30;

Directory Structure

src/
├── lib.rs      # Entry point, Send struct, concurrent send
├── dkim.rs     # DKIM signer with cache
├── error.rs    # Error types
├── parse.rs    # Received header parsing
├── send.rs     # Single domain sending logic
├── smtp.rs     # SMTP connection wrapper
└── reject/     # Bounce email generation
    ├── mod.rs
    ├── create_tar_zstd.rs
    ├── encode_mail.rs
    └── reject_mail.rs

Tech Stack

• mail_send - SMTP protocol
• idot / idns - DNS-over-QUIC for MX lookup
• sk_dkim - DKIM key management
• mail-parser - Email parsing for bounce generation
• papaya - DKIM signer caching
• async-scoped - Scoped async tasks for concurrent sending

About

This project is an open-source component of js0.site ⋅ Refactoring the Internet Plan.

We are redefining the development paradigm of the Internet in a componentized way. Welcome to follow us:

• Google Group
• js0site.bsky.social

smtp_send

支持 DKIM 签名、MX 查询和自动退信处理的 SMTP 邮件发送库。

功能

• DKIM 签名: RSA-SHA256，RFC 6376 头部保护（N+1 签名）
• MX 查询: 通过 idot 使用 DNS-over-QUIC
• 并发发送: 按域名分组并行投递
• 故障转移: 失败时尝试多个 MX 服务器
• 退信处理: 自动生成符合 RFC 5321 的拒信报告
• 循环防护: 检查 Received 头数量（最大 30）及 Auto-Submitted/Return-Path 头
• DKIM 缓存: 签名器 600 秒 TTL 缓存

使用

use smtp_send::Send;
use mail_struct::Mail;

#[tokio::main]
async fn main() {
    // 加载 DKIM 私钥
    let sk = std::fs::read("private.key").unwrap();
    
    // 创建发送器，指定 DKIM 选择器
    let sender = Send::new("default", &sk);
    
    // 构建邮件
    let mut mail = Mail::new(
        "sender@example.com",
        ["recipient@example.com"],
        b"Subject: Test\r\n\r\nHello".to_vec(),
    ).unwrap();
    
    // 发送邮件
    let result = sender.send(&mut mail).await;
    
    println!("成功: {}, 错误: {}", result.success, result.error_li.len());
}

API

Send

pub struct Send {
    pub selector: String,  // DKIM 选择器
    pub sk: Sk,            // DKIM 私钥
}

impl Send {
    // 创建发送器
    fn new(selector: impl Into<String>, sk: impl AsRef<[u8]>) -> Self;
    
    // 发送邮件，自动添加 Received 头和 DKIM 签名
    async fn send(&self, mail: &mut Mail) -> SendResult;
}

SendResult

pub struct SendResult {
    pub success: usize,        // 成功投递数
    pub error_li: Vec<Error>,  // 错误列表
}

Error

独立函数

// 不添加 Received 头直接发送
pub async fn send(mail: &Mail, signer: Option<&Signer>) -> SendResult;

// 创建 DKIM 签名器（带缓存），失败返回 None
pub fn signer(selector: &str, host: &str, sk: &Sk) -> Option<RefVal<String, Signer>>;

// 检查 Received 头是否超限
pub fn recv_overflow(body: &[u8]) -> bool;

// 添加 Received 头
pub fn add_received(body: &mut Vec<u8>, from: &str, by: &str);

pub const MAX_RECEIVED: usize = 30;

目录结构

src/
├── lib.rs      # 入口，Send 结构体，并发发送
├── dkim.rs     # DKIM 签名器及缓存
├── error.rs    # 错误类型
├── parse.rs    # Received 头解析
├── send.rs     # 单域名发送逻辑
├── smtp.rs     # SMTP 连接封装
└── reject/     # 退信生成
    ├── mod.rs
    ├── create_tar_zstd.rs
    ├── encode_mail.rs
    └── reject_mail.rs

技术栈

• mail_send - SMTP 协议
• idot / idns - DNS-over-QUIC MX 查询
• sk_dkim - DKIM 密钥管理
• mail-parser - 邮件解析（用于退信生成）
• papaya - DKIM 签名器缓存
• async-scoped - 作用域异步任务，用于并发发送

关于

本项目为 js0.site ⋅ 重构互联网计划 的开源组件。

我们正在以组件化的方式重新定义互联网的开发范式，欢迎关注：

• 谷歌邮件列表
• js0site.bsky.social