What’s the difference between SMTP, IMAP, and POP3?
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You've got three email protocols, and they do three very different jobs. Mixing them up is one of the most common points of confusion for anyone setting up email infrastructure for the first time.
SMTP (Simple Mail Transfer Protocol) is the protocol that sends email. When you hit send, your email client or app uses SMTP to push that message out to a mail server, which then hands it off to the next server, and eventually to the recipient's inbox. It's a one-way street for outbound mail. Ports 25, 465, and 587 are the ones you'll typically see for SMTP.
IMAP (Internet Message Access Protocol) is how you read your email without removing it from the server. Your inbox stays synced across every device you use. Read a message on your phone, and it shows as read on your laptop too. That's IMAP doing its job. It's the default for most modern email clients because it keeps everything in sync. Port 993 is the standard for secure IMAP.
POP3 (Post Office Protocol version 3) is the older approach to reading email. It downloads messages to your device and, by default, deletes them from the server. You get your mail on one device, and it's gone from everywhere else. It still has uses (offline access, low server storage setups), but it's largely been replaced by IMAP for everyday use. Port 995 is standard for secure POP3.
A quick way to keep them straight:
- SMTP sends email out
- IMAP reads email and keeps it on the server (synced across devices)
- POP3 downloads email to one device (and usually removes it from the server)
For deliverability purposes, SMTP is the one that actually matters most. How your SMTP connection is configured, which IP it sends from, whether it's authenticated with SPF and DKIM, all of that shapes whether your email lands in the inbox. IMAP and POP3 are on the receiving end, so they don't affect your sender reputation directly.
If you're setting up your own mail server or troubleshooting why outbound mail isn't working, our free Email Header Analyzer can help you trace exactly what happened at the SMTP layer.
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