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SESK: Stuff Everyone Should Know · sesk.info/aplus-imap-port

Which email retrieval protocol uses port 143 by default?

IMAP (Internet Message Access Protocol) uses port 143.

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  1. IMAP ✔
  2. POP3
  3. SMTP

Why: IMAP is registered to port 143. POP3 uses 110 and SMTP uses 25. IMAP is the one meant for reading mail that stays on the server.

Huh, didn't know that: The IANA entry cites RFC 3501 and the newer RFC 9051 for IMAP.

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References

Answer: IMAP. IMAP is registered to port 143. POP3 uses 110 and SMTP uses 25. IMAP is the one meant for reading mail that stays on the server.

  1. RFC 9051: Internet Message Access Protocol (IMAP) - Version 4rev2, IETF www.rfc-editor.org/rfc/rfc9051.txt
    When TCP is used, an IMAP4rev2 server listens on port 143 (cleartext port) or port 993 (Implicit TLS port).
    Checked 2026-10-11.

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