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Email Protocols
SMTP pushes mail between servers; IMAP/POP3 pull it to clients. SPF, DKIM and DMARC stop spoofing.
// mail delivery path
Sender MUA
587 ▶ MSA
→ MTA
25 ▶ MX / MTA
→ MDA
993 ◀ Recipient MUA
MUA = mail client · MSA = submission · MTA = transfer · MDA = delivery. The recipient pulls with IMAP (993) or POP3 (995).
// protocols & ports
| SMTP | TCP 25 | Server-to-server relay (MTA → MTA) |
| SMTP submission | TCP 587 | Client sends mail (STARTTLS) |
| SMTPS | TCP 465 | Implicit-TLS submission |
| POP3 | TCP 110 / 995 | Download & (usually) delete |
| IMAP | TCP 143 / 993 | Sync mailbox across devices |
// anti-spoofing
| SPF | TXT record listing IPs allowed to send for the domain |
| DKIM | Cryptographic signature in headers, verified via DNS key |
| DMARC | Policy (none/quarantine/reject) + reporting; aligns SPF & DKIM |
| DANE / MTA-STS | Enforce TLS for mail transport |