#Mail Server

A mail server implementation in Rust with support for SMTP, POP3, and IMAP protocols with TLS/STARTTLS support.

#Features

• ✅ Basic SMTP protocol support (HELO/EHLO, MAIL FROM, RCPT TO, DATA, QUIT)
• ✅ STARTTLS support for secure connections
• ✅ Self-signed certificate generation for TLS
• ✅ Async/await with Tokio runtime
• ✅ Structured logging with tracing
• ✅ Multiple recipient support
• ✅ Command validation and error handling

#Running the Server

cargo run

The server listens on 127.0.0.1:2525 by default.

#Testing

You can test the server using nc (netcat) or telnet:

echo -e "EHLO test.com\r\nMAIL FROM: <sender@example.com>\r\nRCPT TO: <recipient@example.com>\r\nDATA\r\nSubject: Test\r\n\r\nTest message\r\n.\r\nQUIT\r\n" | nc localhost 2525

#Supported Commands

• HELO/EHLO - Initiate SMTP session
• MAIL FROM - Specify sender email address
• RCPT TO - Specify recipient email address (supports multiple)
• DATA - Begin email message content
• RSET - Reset the current transaction
• NOOP - No operation (keepalive)
• QUIT - Close connection
• STARTTLS - Upgrade connection to TLS

#Building

cargo build --release

#POP3 Protocol Support

This repository includes comprehensive examples and documentation for the POP3 (Post Office Protocol version 3) implementation.

#POP3 Features

• ✅ USER/PASS authentication
• ✅ STAT command for mailbox statistics
• ✅ LIST command for message listing
• ✅ RETR command for message retrieval
• ✅ DELE command for message deletion
• ✅ RSET command to unmark deletions
• ✅ NOOP keepalive command
• ✅ Optional TLS/SSL support (POP3S)

#POP3 Examples

The repository includes comprehensive POP3 examples:

#Rust Examples

# Run the POP3 client example
cargo run --example pop3_client

# Run the POP3 server example
cargo run --example pop3_server

# Run integration tests
cargo run --example pop3_integration_test

#Python Example

# Run the Python POP3 client
python3 docs/scripts/pop3-client.py

#Manual Testing with netcat

# Connect to POP3 server
nc localhost 110

# Then type commands:
USER testuser
PASS testpass
STAT
LIST
RETR 1
QUIT

#POP3 Documentation

For comprehensive POP3 documentation, see docs/POP3.md, which includes:

• Protocol basics and command reference
• Setup and configuration guide
• Usage examples for clients and servers
• Unit and integration testing examples
• Integration with SMTP and IMAP
• Troubleshooting guide
• Best practices for security and performance

#POP3 Quick Start

// Example: Connect to POP3 server and retrieve messages
use std::io::{BufRead, BufReader, Write};
use std::net::TcpStream;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut stream = TcpStream::connect("localhost:110")?;
    let mut reader = BufReader::new(stream.try_clone()?);

    // Read greeting
    let mut greeting = String::new();
    reader.read_line(&mut greeting)?;
    println!("{}", greeting);

    // Authenticate
    writeln!(stream, "USER testuser")?;
    let mut response = String::new();
    reader.read_line(&mut response)?;

    writeln!(stream, "PASS testpass")?;
    response.clear();
    reader.read_line(&mut response)?;

    // Get mailbox statistics
    writeln!(stream, "STAT")?;
    response.clear();
    reader.read_line(&mut response)?;
    println!("{}", response);

    // Close connection
    writeln!(stream, "QUIT")?;

    Ok(())
}

See examples/pop3_client.rs for a complete client implementation with all POP3 commands.

#Dependencies

• tokio - Async runtime
• anyhow - Error handling
• tracing / tracing-subscriber - Logging
• regex - SMTP command parsing
• native-tls / tokio-native-tls - TLS support
• openssl - Certificate generation
• futures - Stream handling
• tokio-util - Codec utilities