Glossary · Email

POP3 (Post Office Protocol version 3)

POP3 is an older email retrieval protocol that downloads messages from a server to one device, usually removing them from the server afterwards.

Updated October 6, 2026

POP3 (Post Office Protocol version 3) is a protocol for retrieving email in which the client connects, downloads waiting messages and, by default, deletes them from the server. It was designed for users who dialled in occasionally and kept mail on a single computer.

Why it matters

POP3 still appears in legacy setups, in tools that import mail into another system and on servers with tiny quotas. Its limits are the reason IMAP took over: POP3 has no real concept of server-side folders, and read state is not shared between devices. If a client downloads and deletes mail, other devices never see it.

Example

Standard ports: 110 for plain POP3 (upgradeable with STARTTLS) and 995 for POP3 over TLS.

Incoming (POP3): pop.example.com
Port: 995  Security: SSL/TLS
Option: Leave a copy of messages on the server

The last option is what stops a second device from finding an empty mailbox.

Common mistakes

  • Leaving the default delete-after-download setting on while also checking mail from a phone.
  • Expecting sent mail or folder changes to sync; POP3 only handles retrieval of the inbox.
  • Believing POP3 is insecure by definition. Over TLS the connection is protected; the problem is the sync model, not the transport.

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