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What You Need to Know About IMAP Internet Standard

Internet Message Access Protocol (IMAP) is an Internet standard protocol used by email clients to retrieve mail from a server over a TCP/IP connection.

IMAP, also known as Internet Message Access Protocol is an application-layer Internet standard protocol that is used by email clients to retrieve e-mail from a mail server over a TCP/IP connection.

IMAP Internet Protocol Background

IMAP was designed to allow the complete management of a mailbox by multiple email clients. For this reason, email messages are generally left on the server until the user explicitly deletes them.

An IMAP server typically listens on port number 143. IMAP over SSL/TLS (IMAPS) usually happens on port number 993. STARTTLS is also supported by this protocol.

This protocol was published in 1986 as a remote access mailbox protocol. IMAP2 was published in 1988 and updated in 1990. IMAP3 was published in 1991. IMAP2bis was published in 1993 which was renamed IMAP4.


  • IDLE: This enables real-time notifications of the received emails.
  • SORT: This sorts messages at the server so the email program can fetch certain ones without downloading all of them.
  • THREAD: Allows email clients to retrieve related messages without downloading all mail in a folder.
  • CHILDREN: This allows the implementation of a hierarchy of folders.
  • Access Control List (ACL): This specifies rights for individual users in each IMAP folder.

IMAP Strengths

Typically, email messages are stored and organized in folders on an email server. The Email clients on end-users’ computers and mobile devices replicate that structure and synchronize actions on these folders.

These could be anything from deleting or moving messages between these folders. Each client connected to the same IMAP server will have the same synchronized view.


IMAP is a more complex and difficult protocol to implement resulting in email clients and servers differing in how they interpret the standard.

If you send a message through SMTP from an IMAP connected client, it must be transmitted again through IMAP to be stored in the Sent folder of the IMAP account.

All the synchronization going on may result in users finding email functionality slow and sometimes unreliable.

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