#SMTP and IMAP Mail Server

A basic SMTP and IMAP server implementation in Rust with TLS/STARTTLS support.

#Features

#SMTP

• ✅ 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
• ✅ Dual-mode operation: separate ports for incoming and outgoing mail

#IMAP

• ✅ IMAP4rev1 protocol implementation
• ✅ Essential commands (LOGIN, SELECT, EXAMINE, FETCH, SEARCH, LIST, STATUS, LOGOUT, CAPABILITY)
• ✅ Mailbox management (INBOX, Sent, Drafts, Trash)
• ✅ Message storage and retrieval
• ✅ UID and sequence number support
• ✅ Message flags (Seen, Answered, Flagged, Deleted, Draft, Recent)
• ✅ Protocol state management

#General

• ✅ Async/await with Tokio runtime
• ✅ Structured logging with tracing
• ✅ Shared message storage between SMTP and IMAP

#Running the Server

cargo run

The SMTP server listens on two ports: - 127.0.0.1:2525 - Receive mode: For incoming mail from other servers (messages stored in INBOX) - 127.0.0.1:2526 - Submit mode: For outgoing mail submission from clients (messages logged and relayed)

The IMAP server listens on 127.0.0.1:1143 by default.

#Testing

#Testing SMTP

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

Testing receive mode (port 2525): bash 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

Testing submit mode (port 2526): bash echo -e "EHLO test.com\r\nMAIL FROM: <sender@example.com>\r\nRCPT TO: <recipient@example.com>\r\nDATA\r\nSubject: Outgoing Test\r\n\r\nOutgoing message\r\n.\r\nQUIT\r\n" | nc localhost 2526

#Testing IMAP

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

# Connect and login
echo -e "a1 CAPABILITY\r\na2 LOGIN user pass\r\na3 LIST \"\" \"*\"\r\na4 SELECT INBOX\r\na5 LOGOUT\r\n" | nc localhost 1143

# Fetch messages
echo -e "a1 LOGIN user pass\r\na2 SELECT INBOX\r\na3 FETCH 1 (FLAGS BODY[])\r\na4 LOGOUT\r\n" | nc localhost 1143

#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

#IMAP Commands

• CAPABILITY - List server capabilities
• LOGIN - Authenticate user
• LIST/LSUB - List available mailboxes
• SELECT - Select a mailbox (read-write)
• EXAMINE - Select a mailbox (read-only)
• FETCH - Retrieve message data
• SEARCH - Search for messages
• STATUS - Get mailbox status
• LOGOUT - Close connection
• NOOP - No operation (keepalive)

#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