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~/glossary / E-mail

IMAP

IMAP (Internet Message Access Protocol) is the protocol mail clients use to read, move and manage messages directly on the server.

daniele@mikweb: ~/glossary — man imap

With IMAP messages stay on the server, and folders and read status are synchronised across all devices. POP3 downloads messages and usually deletes them from the server. For multiple devices, IMAP is the standard today.

IMAP runs on port 143 with STARTTLS or on port 993 with implicit TLS. Sending is not part of IMAP; it goes separately through SMTP submission.

Typical problems: full quota, very large folders that slow down client sync, and login failures after a switch to modern authentication, for example Microsoft 365 requiring OAuth 2.0 instead of a password.

Example

openssl s_client -connect mail.example.com:993 -quiet
daniele@mikweb: ~/glossary — ls

Related terms

SMTPSMTP (Simple Mail Transfer Protocol) is the protocol used to transfer email between mail servers and from mail clients to their server.STARTTLSSTARTTLS is a command that upgrades an initially unencrypted connection (SMTP, IMAP, POP3) to TLS.MTA (mail transfer agent)An MTA (mail transfer agent) is the server software that accepts email over SMTP, queues it and passes it to the next server or the mailbox.CalDAV and CardDAVCalDAV and CardDAV are open protocols built on WebDAV that synchronise calendars (CalDAV) and address books (CardDAV) between a server and devices.

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