How to understand SMTP, POP3, and IMAP

· Category: Networking

Short answer

SMTP sends email. POP3 and IMAP receive email. IMAP keeps messages on the server, while POP3 typically downloads and deletes them.

Key differences

  • SMTP (Simple Mail Transfer Protocol): Used to send outgoing mail from clients to servers and between servers. Operates on ports 25, 587, and 465.
  • POP3 (Post Office Protocol v3): Downloads emails to a single device and usually removes them from the server. Operates on port 110 or 995 with SSL.
  • IMAP (Internet Message Access Protocol): Syncs emails across multiple devices while keeping the master copy on the server. Operates on port 143 or 993 with SSL.

When to use each

  • Use SMTP for all outgoing mail submission.
  • Use IMAP when you check email from multiple devices like phones, laptops, and webmail.
  • Use POP3 rarely, only when you want local-only storage and have a single device.

Why it matters

Choosing the right protocol affects accessibility, storage, and backup strategies. IMAP is the modern standard because it supports multi-device synchronization and server-side organization.