HTTP

  • Web-based email
  • Not made for access other than the web
  • Some HTTP accounts can be checked given the right client tool (like Outlook can check Hotmail)

POP

  • Not made for keeping multiple computers/devices and web in sync
  • Generally, mail is downloaded from the server upon checking it (unless you use a tool like Outlook which has the ability to leave it on the server)
  • Even if you leave messages on the server, if you delete on remote device, it will not delete on the server (unless you have a client tool like Outlook which will give you some options)
  • If you send from remote device, it is not pushed to a sent items folders on the server
  • Only brings messages down in the Inbox (not sub-folders)
  • No good push capability for mobile devices (as of this writing)
  • POP is low cost
  • Most personal email accounts use POP (i.e. Gmail)

IMAP

  • Keeps multiple computers/devices and web in sync
  • Mail is left on the server when checked
  • Inbox and sub-folders are brought down to client machine/device
  • Push mail available on mobile devices, but many complain of poor support
  • Newer than POP
  • Catching on among personal users who do not have Exchange

Exchange

  • The most robust email platform
  • Mail is kept on the server
  • Allows calendar, tasks, notes, etc. in addition to email
  • Allows group collaboration of calendars, etc. when used in a group environment
  • Excellent about keeping everything (PCs/mobile devices/web) in sync
  • Push email for mobile devices (Blackberry and non-Blackberry with Exchange ActiveSync)
  • Pretty much the standard for medium size and enterprise email/collaboration
  • Expensive 
  • Gaining popularity among small businesses and personal users as it becomes more affordable

…maybe, one day, I’ll turn this into a more complete matrix of features to allow for generic comparison.  But I will note that there is a different connotation, a different aura that doesn’t fit into a particular feature list about each of these.  For now, I will suggest that you should use Exchange since you are a blog reader of mine and are therefore technically-savvy, business-savvy, and/or someone who copies what I do since I know what I’m doing.

Update on 7/15/10: I don’t have much time to maintain or update old posts like this, but did want to add that Gmail (and Google Apps) support IMAP and also now support Exchange Active Sync capabilities for certain devices (like the iPhone, but not Outlook unless you have Google Apps Premier Edition). I should also add that I have switched over to Google’s email services at some point last year for a variety of reasons (but mainly for the TCO benefits and wanting to verify the hype). I’ve been pretty happy, but I might consider going back to Exchange one day since I still feel it is the best service. Having good choices is always nice — a little education and a positive attitude is what creates email success, not the technology.