SMTP vs IMAP vs POP3

There are 3 separate protocols that are all related to e-mail in a general sense. One is strictly for sending mail out and two are for receiving e-mail from the server.

  • Simple Message Transfer Protocol – SMTP
  • Internet Message Access Protocol – IMAP
  • Post Office Protocol version 3 – POP3

What SMTP does is allow you to send out a message to your Internet server and from there route around to it’s final destination. Once it arrives at it’s final destination, it’s stored on that mail server until an e-mail client grabs it.

The two major methods of grabbing e-mail from the server are: IMAP (Internet Message Access Protocol) and POP3 (Post Office Protocol version 3).

There are pros and cons to using either e-mail client protocol. And, frankly, it’s a bit confusing as to which is best to use.  The reality is that each protocol has a very real time and place to be used (depending on what you want to do).

POP3 is excellent if all you want to do is pull down mail from the server to a single client. This could be a single desktop computer (perhaps using Outlook or Thunderbird or any other desktop e-mail client).  If you don’t access e-mail from anywhere else, POP3 is fantastic because it’s quick, very simple to set up and it works with everything.

What’s nice with IMAP is that it synchronizes with two or more applications (whether on one computer or several devices).  So, if you have a blackberry or an iPhone or several computers or all of the above and you want to be able to read the same messages from each e-mail client, then IMAP is the system for you.

In addition to synchronization, IMAP allows you to organize a hierarchy of message folders.  So you could have a folder structure that looks like the image below.

Once a message has been moved from one folder, that message reflects across the board to every e-mail client (in the new folder).

This allows for easy message sorting and prioritizing.  Also, this folder hierarchy can be only partially synchronized (if, for example, you only wanted the SPAM folder to be maintained on the server – not your mail clients).

Also, if you have a large inbox (say, larger than 1GB or so), then IMAP allows you to only retrieve the headers (rather than the entire message) from the e-mail server.  So if you have several hundred new messages, retrieving only the headers allows you to sort through them very quickly – instead of having to download everything from every one of them.  Significantly quicker.

If your e-mail style is to maintain an empty inbox (so only several dozen messages get downloaded at a time), then POP3 is actually faster than IMAP because it does not need to filter and sort through all of the folder hierarchy.

One final point to consider with IMAP is this: once a message is marked as read on one client, that message gets marked as read with all of the clients.  This eliminates the need to “clean up” several inboxes every time new messages come in.

For example, let’s say you are out of the office and read a message on your iPhone or BlackBerry, if you are using IMAP as your mail protocol, then on your computer at your desk, that same message will be marked as read when you get back.  With POP3, you would have to read the message in both locations to take the “read” flag off the e-mail.

Those are the basic differences between the e-mail client protocols.

Originally posted on Geek Inc. Blog – Dec 2, 2010