In short: IMAP and POP3 receive email; SMTP sends it. For most people, IMAP with authenticated SMTP is the best choice.
| Protocol | Purpose | When to use it |
|---|---|---|
| IMAP | Keeps messages and folders on the mail server and synchronises changes. | Recommended for phones, laptops and multiple devices. |
| POP3 | Downloads messages to a mail application; retention behaviour depends on the client. | Legacy or single-device workflows with a deliberate local-backup plan. |
| SMTP | Submits outgoing messages to the mail server. | Required for sending, normally with authentication and TLS. |
Why IMAP is normally better
Read status, sent items, folders and deletions remain synchronised between devices. The server copy also makes moving between devices easier. Remember that synchronisation is not the same as a backup: deleting a synchronised message may delete it everywhere.
When POP3 may be appropriate
POP3 can suit a controlled archival workflow in which one computer downloads mail and maintains a separate backup. Check the mail application's “leave messages on server” behaviour before using it.
SMTP authentication
Outgoing mail requires the complete email address and mailbox password. Use the secure submission settings in our email server settings article. Do not use TCP port 25 for an ordinary mail client.
Further reading: InterWorx: Configure an email client.
