Email Protocols: The Difference between IMAP and POP

Most email clients support two main protocols of handling email: POP (Post Office Protocol) and IMAP (Internet Message Access Protocol). While users may elect to use either the POP or IMAP protocol for their email client, ITS strongly recommends the use of IMAP and provides configuration documentation for that protocol only. The differences between these two protocols are detailed below.

The POP protocol is designed for people who access their email primarily on one machine. When connected to an email server, POP will typically download all messages to the local machine, and unless configured not to do so, will delete downloaded messages from the email system. POP is useful with email systems that give users very limited storage for email and where it is likely that a user will be able to download all messages at once.

IMAP is designed to leave copies of email messages on the email server, allowing users to check their messages from multiple locations. When users check their email, only the headers of the incoming messages are initially downloaded; the contents of messages are downloaded when users open particular messages.

Because IMAP clients do not download the entire email message at first, this protocol is appropriate for users who have a persistent Internet connection. Also, because the messages remain on the email server, there is a greater chance that messages that are unintentionally deleted can be restored from system backups (unlike POP clients, which do not offer a large enough window for backups to be processed, since the time between message receipt and removal is a small one).

Both protocols allow users to organize messages into folders. POP folders are stored locally on the user's machine and are limited only by the amount of storage space on the local machine. IMAP folders--although constrained by the storage quotas--offer greater portability, being available from any client that can access the email system.