Computing Service

Email

Reading email - POP and IMAP

POP and IMAP are two different "protocols" for reading and storing mail.

Using IMAP (the Internet Message Access Protocol), your mail is kept at all times on your main mail server (e.g. Hermes). If you move to a different computer (e.g. from Department to College), it makes no difference; you still see the same mail, both stored and incoming. With POP (Post Office Protocol), your incoming mail is normally downloaded to the local computer on which you are reading it. If you move to another computer, you can still read new incoming mail but you no longer have access to the messages you read or sent earlier.

POP is therefore suitable mainly for those who always read their mail from the same location. It is also worth noting that if you use IMAP with a University system then backup copies of your stored mail are kept automatically by the central system (except for messages you have deleted). If you are a POP user then you are responsible for keeping any necessary backups.

It is possible to set up a POP MUA to keep copies of your mail on the server, but this can make the collection of mail very slow and also often causes problems on the server itself.

Most commercial systems, and some of the common email clients, use the POP protocol by default (and very few commercial ISPs support IMAP). All of the mail programs provided on Computing Service systems are set up to use IMAP.

Alpine, PC Pine, pine, Mulberry and (effectively) Webmail are IMAP programs (Mulberry also has a POP option). Eudora, Thunderbird, Apple Mail and Outlook can all support either POP or IMAP; most of them are initially configured for POP.

Managing an IMAP mailbox

  • Maintain your connection to your mail machine while you are working with your mail. Opening an INBOX has an overhead so it is more efficient to stay logged in.
  • Move read mail out of your inbox so that the inbox isn't too large. Opening a large inbox takes time. This is especially important if you are using a dial-up connection.
  • Keep your mailboxes small.

Managing a POP mailbox

  • The mail user agent should not be set to check the mailbox too frequently. Collecting mail once every ten minutes is sensible; collecting mail more than once every five minutes is strongly discouraged.
  • MUAs should not be set to 'leave mail on server'.

The title of this document is: POP and IMAP
URL: http://www.cam.ac.uk/cs/email/popandimap.html