Choose the right email protocol
Choose POP3 or IMAP
Choose between a download-oriented maildrop and a synchronized server-side mailbox.
You’ve now seen both access protocols. Choosing between them comes down to one question: where should the authoritative copy of the mail live?
If the answer is “on this one machine”, pick POP3. If the answer is “on the server, and every device is a view”, pick IMAP. Everything else follows from that.
Neither protocol sends mail. Whatever you pick, your client still uses SMTP submission for outgoing messages.
Side by side
| Question | POP3 | IMAP |
|---|---|---|
| Authoritative copy | Commonly local after download | Server mailbox |
| Shared folders and flags | No standard model | Yes |
| Durable identifier | UIDL per maildrop | UID within UIDVALIDITY |
| Partial fetch and search | Limited | Built in |
| Multi-device conflicts | Client policy | Protocol synchronization |
Don’t decide from the port number or from what a provider enables by default. Decide from the ownership row.
Three scenarios
A monitoring inbox that one daemon reads and processes. Alerts arrive, a script parses them, and they’re archived in a database. POP3 fits. One client, download and delete, small command set, nothing to sync.
A legal archive collector that must keep every message for seven years. Also POP3, or IMAP in read-only EXAMINE mode. The important property is that the archive owns the copy, and nobody’s phone can delete it.
A personal mailbox on a phone, a laptop, and webmail. IMAP, without hesitation. Read state, folders, and sent mail all need to agree across devices, and POP3 has no way to make them agree.
Security isn’t the difference
Both protocols run over TLS today (995 and 993). Both should validate certificates. Neither is “more secure” than the other.
Complexity is the difference. IMAP exposes much more server state because it solves a harder problem: keeping several clients consistent. If you’re implementing a client, an IMAP one is several times the work.
Migrating is not automatic
Here’s a mistake that loses years of mail. Someone switches a POP3 account to IMAP in their mail app, sees an empty server-side inbox, and assumes the old messages are gone.
They aren’t gone. They’re on the local disk, where POP3 put them, and switching protocols doesn’t upload them. To keep them accessible everywhere, drag them into an IMAP folder so the client uploads them with APPEND. Do that before you delete the old account configuration.
Try choosing a protocol for each of the three scenarios above on your own, and write one sentence per scenario about where the authoritative copy lives. If you can’t answer that sentence, you haven’t chosen yet.
Lesson completed