Both POP3 and IMAP are protocols that an email client uses to receive email. An example of an email client is Outlook, Windows Mail, etc.
POP3 – Post Office Protocol 3 is a protocol that has been around for decades. It’s the standard way that a mail service will receive email from a mail server. With Post Office Protocol version 3 (POP3) your mail is saved for you in your mail box on the mail server. When you read your mail, all of it is immediately downloaded to your computer or device and no longer maintained on the mail server.
IMAP – Internet Message Access Protocol is a protocol that is much newer then POP3 and is used by mail products to view your mail as opposed to actually downloading it. IMAP (the latest version is IMAP4) is a client/server protocol in which email is received and held for you by your mail server. IMAP requires continual access to the server during the time that you are working with your mail.
What is the difference to me?
If you decide to configure your email client or mobile device to connect to your mailbox using POP3 then what happens is that the email client or device contacts the mailbox and the contents of the email is downloaded to your local computer or device. The mail then will only exist on that computer/device and would not be available to download via another client or device. It is however worth noting at this point that a number of clients and devices do allow you to enable a setting to "Leave a copy of the email on the server" this would then allow them to be download via a second client if required.
When using IMAP with a client or device, the device simply connects to the mailbox and display the full mailbox to you without actually downloading the content to your local computer or device. This has the benefit of allowing you to manage your mailbox from multiple clients and devices and seeing the same content. IMAP has the additional advantage of allowing you to synchronize with folders in your inbox such as the Junk Mail folder, or any other sub folders you might create.
Which one should you use?
Which protocol you decide to use depends mainly on how you will be accessing and managing your email. If you are likely to be viewing your mail from multiple locations, clients or devices then It is usually best to use IMAP. IMAP will allow you to manage your mailbox from all of these different locations and clients while the actual mailbox content remains on the provider’s mail server. If you were to do the same using POP3 with the "Leave a copy on the server" setting enabled then you are in essence simply creating multiple copies of your mailbox and you would need to ensure that you've setup each client or device to "Leave a copy on the server".
If you are simply going to be using one email client and do not want to worry about reaching the mailbox size limit, due to the amount of email, then POP3 would be the way to go. This provides a simple service to allow you to download all of your mail to one location managed by you. The mailbox on the the mail server would always be empty or close to it as a result and so you would never need to worry about reaching the limit.
If in doubt use IMAP, this gives you the ability to manage your mail from a client or device while still giving the peace of mind that there is a backup copy on the mail server. Keep in mind, however, that you still need to manage your mailbox storage to keep within your mailbox limits. However if you are only accessing your mail from one place and need to keep all your mail locally, POP3 may be a better option.
Please remember that VCG is not responsible for maintaining a backup of any mail left on the mail server, and that we strongly recommend that you maintain your own backup copies on your local computer network.