#Mail Server (SMTP + POP3)

A basic mail server implementation in Rust with SMTP and POP3 protocol support, featuring TLS/STARTTLS support.

#Features

#SMTP Server

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

#POP3 Server

• ✅ Complete POP3 protocol implementation (RFC 1939)
• ✅ User authentication (USER/PASS commands)
• ✅ Message retrieval (STAT, LIST, RETR commands)
• ✅ Message deletion (DELE, RSET commands)
• ✅ Session management (QUIT command with update state)
• ✅ Capability advertisement (CAPA command)
• ✅ Keep-alive support (NOOP command)

#General

• ✅ Async/await with Tokio runtime
• ✅ Structured logging with tracing
• ✅ Shared message storage between protocols
• ✅ Concurrent server operation

#Running the Server

cargo run

The servers listen on: - SMTP: 127.0.0.1:2525 - POP3: 127.0.0.1:2110

#Testing

#SMTP Testing

You can test the SMTP 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

#POP3 Testing

Test POP3 commands:

# List messages
echo -e "USER test\r\nPASS password\r\nLIST\r\nQUIT\r\n" | nc localhost 2110

# Retrieve a message
echo -e "USER test\r\nPASS password\r\nRETR 1\r\nQUIT\r\n" | nc localhost 2110

# Check mailbox statistics
echo -e "USER test\r\nPASS password\r\nSTAT\r\nQUIT\r\n" | nc localhost 2110

# Delete a message
echo -e "USER test\r\nPASS password\r\nDELE 1\r\nQUIT\r\n" | nc localhost 2110

#Supported Commands

#SMTP 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

#POP3 Commands

• USER - Specify username for authentication
• PASS - Provide password for authentication
• STAT - Get mailbox statistics (message count and total size)
• LIST - List messages with sizes (all or specific message)
• RETR - Retrieve a specific message
• DELE - Mark a message for deletion
• NOOP - No operation (keep-alive)
• RSET - Reset session (unmark deleted messages)
• QUIT - End session and apply deletions
• CAPA - List server capabilities

#Building

cargo build --release

#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