Email • Protocols
How Email Servers Work: SMTP, IMAP, POP3 for Developers
Developers integrating email or operating mail servers should know how SMTP, IMAP, and POP3 interact. This primer explains each protocol’s role and key configuration tips.
SMTP — sending email
SMTP handles message transmission between servers and from clients to servers. Typical ports include 25 (server-to-server), 587 (submission with TLS), and 465 (SMTPS/implicit TLS). Configure reverse DNS and SPF to improve trust.
IMAP — read & sync
IMAP keeps messages on the server and synchronizes state across devices. Use IMAP for modern email clients that need read/unread sync, folder support, and search capabilities.
POP3 — download & store
POP3 downloads messages to the client (often removing them from the server). It’s simple and lightweight but lacks multi-device synchronization by default.
Practical tips
- Always enable TLS (STARTTLS or implicit TLS) on submission and retrieval ports.
- Set up SPF, DKIM, and DMARC to protect your domain and improve deliverability.
- Monitor mail queue lengths and bounce rates to detect issues early.
