Introduction to IMAP

INTRODUCTION TO IMAP

If you have used email in the past, you have probably used a service based around the POP mail protocol. A more versatile way of handling mail is available called IMAP which is of particular benefit for those who access their mail from different computers. For example, telecommuters access their mail from home and work, or from work and while traveling. IMAP and POP mailboxes are compared throughout this document to illustrate the power and flexibility gained when using an IMAP mailbox.

How IMAP is different from POP
Using IMAP to access mail from many different places
IMAP and attachments
Deleting messages with IMAP
Moving mail between folders within a mailbox or between different mailboxes

How IMAP is different from POP

POP mailboxes store mail on a server until a user's mail program accesses the box. At that time, all mail in the mailbox in downloaded to the user's machine then deleted from the server. Any mail sorting or archiving happens entirely on the user's personal computer. The mail server is no longer involved. With IMAP, mail is stored on the mail server and can be accessed, read, sorted, and otherwise manipulated while remaining on the server. Mail will not be deleted from the server until the user specifically makes that request. A copy of the mail may also be downloaded to a user's local computer for off-line viewing.

When checking mail in an IMAP mailbox, the user's mail program "synchronizes" with the mail that is on the server. During this synchronization, only the headers (the "From" "To" and "Subject" lines among other things) of each message are transferred instead of the entire body. Since only a small amount of information is being transferred, the contents of the mailboxes can be seen very quickly. Only when a user selects a message is the body of the mail actually downloaded. Unwanted mail can be deleted without downloading the whole message. Important mail can be dealt with immediately and in any order, while less critical messages wait quietly in the wings until they are wanted

It should be noted that the POP protocol does allow copies of messages to be left on the mail server, but these message cannot be manipulated or organized in any meaningful way.

Using IMAP to access mail from many different places.

The greatest strength of IMAP is that the same mail can be accessed from any location because all mail is stored on the server rather than on a user's computer. A user at work can log into her IMAP mailbox, then go home that night and access the same mail from her home machine. She can then take her laptop on a business trip and access all of her mail on the road.

IMAP and attachments.

If a message contains an attachment, that attachment is not downloaded with the body of the message. Instead, an icon for that attachment is displayed within the email and may be downloaded at the convenience of the user. This is of particular importance if the mailbox is being accessed over a slow connection such as a dialup modem or with handheld device that cannot handle large files. The attachment remains on the server, and can be accessed from a computer at a different location at the user's convenience. Compare this to a POP account where all messages (attachments included) are downloaded one after another. If message 7 has a huge attachment, it will need to be downloaded before message 8 can be viewed.

Deleting messages with IMAP.

Deleting mail is a two step process with IMAP. First messages are "marked" for deletion. Messages marked for deletion still exist on the mail server and can be "undeleted" if desired. To permanently remove the message from the server, the "Purge" command is used which removes all messages marked for deletion. Messages can remain marked for deletion indefinitely. Each mail program has its own way of indicating that a message is deleted, but most involve some kind of red "x" icon beside the message.

At first, this two-step deletion process seems cumbersome and unnecessary but it is really quite useful. Unlike POP mailboxes, IMAP mailboxes can be accessed from multiple locations and multiple people can access the mailbox at the same time. Two people looking at the same mail can indicate that they feel a message is no longer needed, by marking it as "deleted" while leaving it in its current location. Other viewers of the same mail may then undelete the message or purge it if they agree that it is not needed.

Moving mail between folders within a mailbox or between different mailboxes

Mail programs that support IMAP can move messages between folders on the mail server; between the mail server and a local mail folder; and even between different IMAP mailboxes on different servers. To understand how IMAP can move mail, it is helpful to look at a few examples. We'll use a fictional user "Jane Doe" who has two IMAP mailboxes. One mailbox is used primarily for her personal correspondence, and the other is for her work email.

Mail programs that support IMAP will display a list of local mail folders and a separate list of IMAP folders. To the right is a screen shot from Eudora displaying three local mail folders: "In", "Out" and "Trash" that only exist on Jane's personal computer. These local folders will exist whether or not Jane also has a POP based mailbox. If she did have a POP mailboxes, all of the POP based mail would go into the uppermost "In" box.

Below the local folders is the listing of Jane's personal IMAP mailbox. Within this IMAP "Inbox" are several folders: "Archive", "Drafts", "Sent" and "Trash" which all exist on the mail server. Jane created the Archive, Drafts, and Sent Folders to aid in mail sorting. Below all of this is the listing containing an Inbox for Jane's work email where she has created a "Sales" folder.

Folders that contain unread mail appear in bold.

Example 1: Jane has received a message from a friend who will be visiting in a few weeks. The message contains flight information that she wants to save for future reference. Rather than having it clutter up her Inbox she drags the message from the Inbox folder of her personal IMAP mailbox to the Archive folder of her personal IMAP mailbox. When she does this, her mail program tells the mail server to move the message on the server from Inbox to Archive, the message in the Inbox is then marked deleted (the message is just marked deleted and is not really removed until Jane uses the purge command) and appears in the Archive folder. Later, Jane will be able to access this mail anywhere she can access her IMAP mailbox.

Example 2: A potential client has sent a business email to Jane's personal mail address. She would like to keep this mail with similar items in the "Sales" folder of her work IMAP mailbox. To do this, she drags the message out of the Inbox of her personal mailbox and into the Sales folder of her work mailbox. With this simple action, Jane has moved the message between two folders in two separate mailboxes on two separate IMAP servers. The IMAP protocol handles all of the necessary transfer steps between these two severs automatically.

Example 3: Jane will be commuting to her home office and won't have Internet access during her ferry ride, but she wants to read her morning email while onboard. Beforehand, she uses her laptop to access her IMAP mailboxes then copies that morning's mail into the local "In" folder (which exists only on her computer). She can now disconnect from the Internet and review these message directly from her laptop without needing Internet access.

Updated 12/09/02 (editorial changes 12/28/02)


	\| OlympusNet Home Page \| Services \| Contact Us \| Help \|