Understanding POP and IMAP

Caution: Because the VT Mail system is not yet appropriately configured for general IMAP use, 4Help strongly recommends you use POP (pop.vt.edu) when you configure your e-mail client to connect to the VT Mail server. Using POP means that you automatically have a local copy of your e-mail on your computer after you have checked your e-mail. If you "pop" your e-mail off of the server using an e-mail client frequently, you will not need to be concerned about the current 32 day mail deletion cycle implemented for storage control. For more information on the 32 day mail expiration, see Mail Storage and Retention. For instructions on how to configure your e-mail client to use POP, see the VT Mail page.

For more information, see Status of IMAP at Virginia Tech.

Introduction

POP and IMAP are both standard e-mail protocols. POP and IMAP deal with the receiving of e-mail from your local server and are not to be confused with SMTP, a protocol for transferring e-mail between points on the Internet. You send e-mail with SMTP and a mail handler receives it on your recipient's behalf. You read e-mail using POP or IMAP. Think of POP as a store-and-forward service and IMAP as a remote file server. The difference lies in how you access and retrieve your mail from the mail server.

POP (Post Office Protocol)

The VT Mail server runs POP which is a very simple mail retrieval protocol that allows your e-mail client, such as Eudora and Outlook Express, to download your messages from the VT Mail server. By default under POP, most e-mail clients remove your e-mail from the server when you check your messages. Since the messages are only stored on your personal computer, storage space on the server is usually not a big issue. You may store as much mail on your personal computer as it can handle. You can configure your e-mail client to leave your messages on the server, if you would like to access your e-mail from several different locations.

IMAP (Internet Message Access Protocol)

IMAP is a more complex mail retrieval protocol in which an e-mail server receives and stores your mail for you, allows you to see the folders you create both in your e-mail client and on the server. By design under IMAP, e-mail clients leave the originals of your messages on the server when you check your messages, downloading only an index. To keep storage requirement from growing beyond control, most IMAP-capable servers have quotas, or limits, on the amount of mail you can store on the server. Once you reach your quota, mail destined for you will not be delivered until you have deleted some e-mail messages and are back under your quota. For more information on quotas, see the Quotas section on the VT Mail Mailbox Management page.

Some IMAP e-mail clients will also keep a local copy of your messages for use if your computer is not online. Be aware, though, that these local copies are not permanent archives and will be synchronized with the server the next time you connect to the server. If you deleted mail from WebMail (the server), your local copies of those messages will disappear. In order to permanently save e-mail in IMAP protocol once you have reached your quota of space on the server, you must download the messages and save them to a folder or removeable media, such as a CD or ZIP drive, or use autoarchive, if your e-mail client offers that feature.

Other advantages of IMAP include viewing only the heading and the sender information of the message and then deciding whether or not to download the whole message. You can also create and manipulate folders or mailboxes on the server, delete messages, or search for certain parts or an entire note.