SMTP, IMAP and POP3 are the three protocols that move email around the internet, and each has a single, distinct job: SMTP sends, IMAP and POP3 retrieve. They are not interchangeable — a working email setup almost always uses SMTP plus one of the other two.
Side-by-side comparison
| Protocol | Direction | Stores mail on server? | Multi-device sync | Default ports |
|---|---|---|---|---|
| SMTP | Sending | N/A (transit only) | N/A | 25, 465, 587 |
| IMAP | Receiving | Yes | Yes — same view everywhere | 143, 993 (TLS) |
| POP3 | Receiving | No (default) | No — downloaded to one device | 110, 995 (TLS) |
SMTP — how email is sent
Simple Mail Transfer Protocol pushes outbound mail from a client (your phone, app, server) to your mail server, then from server to server, until it reaches the recipient’s inbox. It is also the protocol used between mail servers when accepting incoming messages, but end users never use SMTP to read mail.
IMAP — modern multi-device reading
Internet Message Access Protocol keeps your mail on the server. Each device synchronises folders, read/unread state and even drafts in real time. If you read an email on your laptop, it’s already marked as read on your phone.
POP3 — download and forget
Post Office Protocol v3 downloads each message to one device and (by default) deletes it from the server. It’s simple, light on bandwidth, but works poorly when you have several devices or want a backup.
Which one do you need?
- You want to send with Mailpro — SMTP relay.
- You want to read mail on phone + laptop — IMAP.
- You want a single offline copy — POP3, with care.
Set up sending with Mailpro’s SMTP relay
Read about SMTP relay services, find the right SMTP port and check whether SMTP can receive email.