The fundamental difference between IMAP and POP is how messages are transferred, and how long email is stored on the mail server.
When POP is used, messages are "pulled down" from the mail server, and depending on how you have set up your email software, they may or may not be deleted from the server during this process, or following it. Typically, messages are removed from the server either immediately, or after a given time period such as 10 days, once the message has been "POPed" to your email software.
This means your emails are accessible only from the individual computer or device to which they have been downloaded (unless you have specifically set up each device's email program to "leave a copy of the email on the server"). In this regard, if the computer or device that has downloaded all of you email decides to go the way of the dinosaurs, or worse - is stolen, all of your historical emails will be gone - unless of course you have made file backups - which of course you have, haven't you?!!!
While POP conserves your hosting server’s disk resources (less space taken up with saved, old emails which are being downloaded instead), it generally limits how you can access your email. One advantage to note however, is that unlike IMAP, POP does not require a constant connection to the email server while email is being read (useful if you are offline much of the time and only go online to send/receive emails).
When IMAP is used, messages are generally stored permanently on the mail server, but the "header" and "content" of messages are transmitted to email clients (e.g. your phone, your desktop email software such as Outlook, or your smart TV!). This means that they can be accessed by any number of computers or devices as long as the user has the correct login information. In other words, all of your devices - e.g. your desktop, your tablet, your phone - that are connected via IMAP to the email server - will "mirror" the other in terms of your email. In this respect, if you delete a message on your computer email software for example, it will also be deleted from your phone and the server and visa versa etc.
IMAP is generally considered quite convenient since you can access the same inbox or outbox from multiple devices. However, IMAP generally requires more dedicated disk space because messages are not being actually downloaded or deleted in the same manner as they are in a typical POP scenario. Therefore, IMAP is great, so long as users monitor their disk usage and continues to delete old are unwanted messages when necessary. It may also be important to note that IMAP requires a constant connection to the email server while email is being read - so it is not suitable for users that frequently go offline for long periods.
The Best Solution?
Use POP AND IMAP by sending and receiving your email via our servers, but through Gmail or Google Apps. With this solution, you will never need to delete old emails! Click here to find out how to set this up.
If you are having difficulty deciding what email service to use, just let us know via a support ticket and we can help you decide.