SMTP, POP3 and IMAP for Email
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Three Protocols, One Goal: Moving Email
Email relies on several different protocols working together, each responsible for a different part of sending or retrieving a message.
SMTP: Sending Mail
SMTP (Simple Mail Transfer Protocol) is used to send email - both from a user's mail client to their outgoing mail server, and between mail servers as a message hops toward its final destination. SMTP only handles sending; it plays no role in a user reading their inbox.
POP3: Download and Remove
POP3 (Post Office Protocol version 3) downloads email from the server to a single device, and by default, removes it from the server afterward. This made sense when people checked email from one computer, but poorly fits a world where the same inbox is checked from a phone, laptop and tablet.
IMAP: Keep Everything Synced
IMAP (Internet Message Access Protocol) keeps email stored on the server and simply lets multiple devices view and manage the same mailbox in sync - read a message on your phone, and it shows as read on your laptop too, since both are viewing the same server-side copy.
Comparing the Three
| Protocol | Job | Where mail lives |
|---|---|---|
| SMTP | Sending mail | N/A - just delivers it onward |
| POP3 | Retrieving mail | Downloaded to one device, often removed from server |
| IMAP | Retrieving mail | Stays on the server, synced across devices |
Why IMAP Is the Modern Default
With most people checking email across several devices, IMAP's server-side synchronization fits modern usage far better than POP3's single-device download model - which is why nearly every modern email client and provider defaults to IMAP today.