Remote Mail: POP vs. IMAP

Currently, two standards exist for the remote retrieval of Internet mail: POP and IMAP.

POP Description

POP (Post Office Protocol) is the most popular service. The most common variant (POP3) operates using TCP on TCP/IP port 110. An older variant (POP2) operated on port 109. The popular Qualcomm "popper" server daemon also supports password changes, which is accomplished through a "poppassd" daemon operating on port 106.

Some popular client programs that support the POP protocol are:

Qualcomm's Eudora program
Pegasus
Netscape Mail
Microsoft Internet Mail
Microsoft Exchange/Outlook
TeamWare's Embla

IMAP Description

The IMAP (Internet Message Access Protocol) is a newer standard which is currently at version 4.1. The protocol itself is under active development by the University of Washington. IMAP operates on using TCP on TCP/IP port 143.

Some popular IMAP client programs are:

Netscape Communicator
TeamWare's Embla
PC-Pine
Coming soon to Microsoft Exchange (planned for Version 6)

Common Traits

Both systems support offline modes of operation.
Mail is accessible from a wide variety of client platforms.
Mail is accessible from anywhere in network.
Both protocols are open and defined by Internet RFCs.
Both systems have Freely available implementations (including source).
Clients E-Mail programs are available for PCs, Macs, and Unix.
There are commercial implementations available.
Both protocols deal with access only; both rely on SMTP to send.
Both support persistent message IDs (for disconnected operation).

POP Benefits

POP is the Simpler protocol; much easier to implement.
More client software currently available.

IMAP Benefits

Can manipulate persistent message status flags.
Can store messages as well as fetch them.
Can support concurrent updates and access to shared mailboxes.
Especially useful management over low-speed links.

Summary

POP is the simplest protocol to implement. It is the most widely used system at the time of this writing. It is less taxing to the server. POP transfers the entire pending queue of mail messages (e.g. you have to download that huge attachment before proceeding on to subsequent messages). If mail is stored on the server, possible sequencing problems can occur if mail is checked from multiple PCs.

IMAP is more taxing to the mail server. E-Mail stays on the system in the mailbox. E-Mail message information is made available to the client. The end-user can selectively read (and download) messages. Also, IMAP allows the user to create mailbox "folders" in the user's home directory. Mail messages (including attachments) can be transferred to the server folder without occupying bandwidth on the dial-up connection.

IMAP permits multiple, simultaneous access to a single mailbox. This is extremely useful for business where multiple individuals have access to a single mailbox.

Conclusion

We suggest that businesses move towards IMAP E-Mail service. It provides more reliable transport (fewer timeout conditions) and efficiently presents message headers without retreiving the actual message. This allows the most efficient use of your connection time.

Look for IMAP coming soon to Microsoft Exchange. It is currently available for Netscape Communicator (sloooow). TeamWare's Embla program is freeware and is an excellent IMAP or POP client.