I get this question a lot.
“What is the difference between POP3 and IMAP? I get my mail, who cares how it happens.”
Well, yes, but the magic is behind the protocol.
POP has been around since email was a thing. POP stands for “Post Office Protocol” and POP3 is just version 3 of the Protocol.
IMAP has been around nearly as long, and stands for “Internet Message Access Protocol“. The two can be used interchangeably on the same email account but one should be warned. POP takes the email off the server onto your device, IMAP is a remote access version of your email box.
Let’s look at an analogy. You access your email on you device through an email client. This could be Microsoft Outlook, Mozilla Thunderbird or Opera Mail or any of them, really. The email server is your email provider, like Yahoo, GMail, Outlook.com, or another provider.
The email client is synonymous to your eyes. You view you email with your client or your eyes.
The email server is your local post office. Your post office keeps all your mail in your PO Box. In this case the PO Box is synonymous to your email account. Your email account is something like email@example.com.
In IMAP instances, you go to your Post Office (email server), open your PO Box (use your password on your email account), take all the mail out and run to the copy machine and copy it all (download the email). You put the originals back into your PO Box and close and lock it, taking the copies with. In this instance IMAP email needs a larger PO Box, so your PO Box would be much bigger. In IMAP protocols, this allows you to view your same email in multiple locations, like on your PC then on your phone.
In POP instance, you do the same thing, but instead of copying email, you simply remove it all from the PO box. This enables you to have a smaller PO Box than your IMAP but at a cost…once the email is downloaded to your PC or mobile device, it’s on there and only there – you can’t view it anywhere else.
POP was popular with email providers many years ago, before the invention of GB and TB hard drives. POP allowed the email provider to give you only a small amount of space to store your email temporarily, usually not more than 10MB. Once the email was downloaded onto your PC, the local copy on the server was deleted, so the space was able to be freed up. Providers didn’t have enough storage for 500,000 email accounts using 10GB (as much as GMail provides you now) back then, as that would have needed 5,000 TB of storage space! Now that we have the technology to easily cluster servers, and large enough hard drives to store all that data, IMAP has quickly replaced POP, especially with many needs to view and access email from multiple devices.