SMTP

  1. SMTP

SMTP

  • TCP 25
  • client-server, RFC 822
  • reply codes:
    • 2**: success
      • 250 = OK
    • 3**: redirection
      • 254 = send next chunk
    • 4**: temporary failure
      • 452 = mailbox full
    • 5**: permanent failure
      • 550 = fatal error
  • DNS MX contains mail server FQDN and priority (lower – better)
  • DNS A for domain – fallback if MX record not found
  • server puts email (data) into envelope that is responsible for delivery
  • commands
    • HELO/EHLO <src domain>
    • MAIL FROM
    • RCPT TO
    • DATA: end of message marked by line with ‘.’ only
    • STARTTLS
    • QUIT