When setting an e-mail account up, most e-mail programs will give you the option to choose between creating a POP (also referred to as POP3) or IMAP account. This always leads to the simple, yet important question: "What's the difference?".
POP accounts are configured to download messages to your computer and then remove the downloaded copies from the mail server thereafter. Effectively, e-mail will only reside on the server until such time as it has been downloaded.
You also have the option to configure your e-mail program to "tell" the server when to delete the messages. This is useful if you access the account from another computer or device as a copy will remain on the server so that both can receive mail. The added benefit is that the disk space allocated to both your mailbox as well as your hosting package is automatically freed whenever the messages are removed.
If you primarily check your mail on your computer or laptop and only use your phone or tablet to notify you when new messages have arrived, then a POP mailbox will do the trick.
Note: Even though the messages have been removed from the server, they will not be removed from your computer.
IMAP accounts were designed primarily because of the need for e-mail accounts to be shared by more than one person - particularly in large corporate environments. What makes IMAP ideal for this is that any changes made to the account by one person (e.g.: sending an e-mail) will be seen by other people even though they are accessing the account from another computer. Essentially, e-mail across all of the computers involved is synchronised.
IMAP does this by keeping a copy of all messages on the mail server. These messages are only removed if you either delete them using your e-mail program or via the webmail platform. IMAP is perfect if you use more than one device to access your e-mail and want your messages to be synchronised across all of your devices.
Note: Because IMAP does not remove mail from the server, the amount of disk space used by your e-mail account will increase as time goes by. This can result in either your mailbox on the server or all of the disk space allocated to your hosting account being used up. Should this happen, then you will either need to remove older messages or upgrade your hosting package.