When setting up your email client on a new computer, or when upgrading to new email software, you will have to set up your email account.
Many new versions of email clients (Windows Live, Outlook, Apple Mail, Thunderbird), and mobile devices make users default to an IMAP configuration. The default Email client that comes with Windows 8 does not even allow a POP set up.
But depending on how you use your email, or want to manage your email, IMAP may not be best for you.
When setting up your email client, ask yourself these questions:
1) Do you absolutely have to have your email available to you at all times (Inbox, Sent Email, Drafts) across all devices (desktop at work, laptop for the road, smart phone)?
IMAP will allow that, but POP3 allows you to see the most recent emails across all devices, if you configure your email client correctly, and that may be all you need.
2) Do you need to be able to view your email even when you have no connection to the internet?
If you do, then it's best to go with an POP3 Email configuation. POP3 automatically downloads copies of your incoming email to your local computer, smartphone or laptop. IMAP requires that you do that manually. If you don't have a connection to the internet, IMAP's Inbox, Sent Email and Drafts folders will not be available to you, unless you have already moved those messages to local folders on your local computer, smart phone or laptop.
To allow your other devices, like SmartPhones and tablet computers, to also access your email, you can simply set POP3 to "leave a copy of the message on the server" for a certain period of time: 2 days, 5 days, 7 days, 14 days. This "window of time" allows you to check your email box with a phone, and your tablet, download the "new" email to view it, even though it's already been downloaded to your main computer.
POP3 will then delete messages off the server that have been downloaded to your local computer, AUTOMATICALLY, so you don't have to worry about it.
With IMAP, if you want a copy of your email on your local computer, you have to move the messages manually into local folders in your email program (Outlook, Apple mail, Thunderbird, etc)
IMAP can be very useful if you have simple emails going back and forth, that you want to be able to check wherever you are. If you are changing devices all the time, and want to "check messages" from anywhere, on any device, it is easy to set up and see your email instantly on your new device.
However, if you are sending and receiving large files, IMAP is probably not the setup for you. You will probably start reaching the upper limits of your server capacity after a while. And the only way to reduce the size of your IMAP folders, is to move the mail MANUALLY. This can be tiresome for some people.
If you have to have your email available to you on every device, and you also want to have more disk space, as well as the ability to sync your calendars and other documents online, you might find that an "Exchange Hosting" solution is best for you.
You can also simply set your email client up to use IMAP and pay for more space "in the Cloud" on the server, as you need it.
if you'd rather save money on "cloud storage", you can simply set your email client up as POP3, which will consistently download your email off the server, and create an archive of your email on one, or more, local hard drives. POP downloads the NEW email off the server, and when COMPOSING and SENDING mail for the outbox, it gets stored locally on your computer, never on the server. You will want to make sure to BACK UP your local computer when storing all your email on your computer, as you will NOT have a back up on a remote server. Even IMAP won't have ALL your emai, unless you purchase more server space. Generally, only your most recent email will be available, depending on the size of your Email Box. A Backup is always a good idea.