Quiz Entry - updated: 2026.07.14
What are the email protocols and how do they work together?
SMTP (port 25) sends mail to and between servers; POP3 (110) downloads and deletes it from the server, while IMAP (143) keeps the originals on the server and syncs across devices.
Email Protocols:
Email is a store-and-forward method of sending, storing, and retrieving electronic messages. Messages are stored in databases on mail servers.
Sending Email - SMTP:
- SMTP (Simple Mail Transfer Protocol) - TCP port 25
- Used by clients to send email to mail servers
- Used between mail servers to relay email
Receiving Email - Two Options:
| Protocol | Port | Behavior |
|---|---|---|
| POP3 | TCP 110 | Downloads mail, deletes from server |
| IMAP | TCP 143 | Downloads copy, keeps on server |
Email Flow:
Sender → SMTP → Mail Server A → SMTP → Mail Server B → IMAP/POP → Recipient
POP vs IMAP:
- POP: Not recommended for businesses needing centralized backup (mail deleted from server)
- IMAP: Better for accessing email from multiple devices (original stays on server, synchronizes deletions)
Go deeper:
-
How Email Works: SMTP, IMAP & POP3 Explained — the send vs retrieve split in one walkthrough. -
Simple Mail Transfer Protocol (Wikipedia) — the push protocol that moves and relays mail.