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What is the difference between POP3, IMAP and Exchange?
Posted by James Robshaw on 21 February 2013 08:58 AM

It is important to understand the fundamental differences between the various E-mail connection protocols in order to choose the one which best suits your needs:


When using POP3 (Post Office Protocol, version 3), all of the messages are downloaded from the mailserver and saved locally. Your E-mail is only accessible from one computer/device and Incoming Mail is no longer available when using WebMail or any other computer/device (unless configured otherwise).


  • Mail always available on the computer/device for offline consultation


  • Sent Items available locally ONLY (no copy exists at all times on the mailserver);
  • Speed of mail download dependent on bandwidth (large attachments may take some time).


IMAP (Internet Message Access Protocol, currently version 4) has features found in both POP3 and Exchange protocols.

When using IMAP, your Inbox is stored on the mailserver whereas the Sent Items are still stored locally (unless otherwise specified). When you check your mail, your computer contacts the mailserver to show you the new Incoming Mail. All of your Inbox is available from any computer and you can check it from anywhere in the world by using WebMail.


  • Incoming Mail always available on multiple computers and/or WebMail.


  • Sent Items available locally ONLY (no copy exists at all times on the mailserver).


  • Because IMAP keeps mail on the server until you delete it, you may potentially run out of disk space if you save a lot of messages especially if large files are attached to them. You must manually remove messages or save them to your local hard drive in order to clear up space on the server. Also because IMAP keeps mail on the server, a recent backup of your e-mail is always available since ProExe's central computers are backed up on a daily basis.

MS Exchange

This protocol has been introduced by Microsoft and is proprietary. All the E-mail (Incoming and Sent Items) is stored on the central Exchange mailserver, where it can be checked using a capable mail client (such as MS Outlook or most current mobile devices) or via WebMail. You may have the option of storing messages in local folders locally for offline consultation (often referred to as "Cached Mode").

Exchange also permits syncing of Calendar and Contacts.


  • Incoming Mail and Sent Items always available on multiple computers and/or Webmail (mail is synced between mailserver and client);
  • Supported by most current mobile devices (tablets, pads, smartphones);
  • Calendar and Contacts synced as well.


  • Not all computer mail clients support MS Exchange Mode (in Windows only MS Outlook, in MacOS Apple Mail and MS Outlook);


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