What is the key difference between POP3 and IMAP for retrieving email?
POP3 downloads messages and then deletes them from the server, while IMAP keeps the originals on the server and synchronizes changes — so IMAP works far better when you read mail on multiple devices.
Both protocols let a mail client pull messages off a server, and the real difference is what happens to the server's copy afterward. POP3 (Post Office Protocol v3) treats the server as a temporary spool: it downloads everything to the one device and removes it from the server, which is fine for a single computer but loses messages for any other device. IMAP (Internet Message Access Protocol) treats the server as the master store: it downloads copies and leaves the originals in place, then mirrors your reads, moves, and deletes back to the server, so every device sees the same mailbox.
* POP3 downloads then deletes from the server; IMAP keeps the originals and syncs every device. *
Both protocols let a client retrieve email from a mail server, but they handle the stored copy very differently.
POP3 (Post Office Protocol v3) — TCP 110:
- The server listens passively on TCP port 110 for client connections.
- When the client connects, the server sends a greeting, then the two exchange commands and responses.
- Mail is downloaded to the client and then deleted from the server.
- Because nothing stays on the server, POP3 is not recommended where a centralized backup is needed (e.g., a small business).
IMAP (Internet Message Access Protocol) — TCP 143:
- When a user connects, copies of the messages are downloaded to the client.
- The original messages stay on the server until the user deletes them manually.
- When the user deletes a message, the server synchronizes that action and removes it on the server too.
| POP3 | IMAP | |
|---|---|---|
| Server copy after download | Deleted | Kept (synced) |
| Multi-device access | Poor | Good |
| Centralized backup | No | Yes |
Why it matters: If you check the same mailbox from a phone and a laptop, POP3 can leave each device with a different, incomplete set of messages; IMAP keeps every device in sync with the server.
Go deeper:
-
Internet Message Access Protocol (Wikipedia) — server-side storage and multi-device sync. -
Post Office Protocol (Wikipedia) — the simpler download-and-delete model on TCP 110.