Both POP (Post Office Protocol) and IMAP (Internet Message access protocol) are ways of getting your email from a remote server. The difference between the two protocols is in the way your device interact with the server.

POP

POP simply downloads the emails from the server to your local device. Those emails are deleted from the server once they downloaded to your device (most of the times). This will save you valuable storage on the server.
So simple speaking POP emails are stored on your device.

The problem with POP is when you have multiple devices which is very common now-a-days. Sent, read, unread emails are not synchronized between your devices.
For example, when you send an email to someone from a computer, that email will be saved on the “Sent” folder of that computer but it will not be visible on the “Sent” folder on the server. This means, if you have another device such as a smartphone, you will NOT see that email on the “Sent” folder of your smartphone.
So simply speaking, that email will only be stored on that device.
Another problem with POP is not synchronizing read and unread emails. For example, let’s assume that you received an email and that email gets downloaded to both your phone and computer. This new email will be shown as unread on both your devices. When you read the email on your computer, it will show as “Read” on your computer but it will still be “Unread” on your smartphone. The reason for this is because you have two copies of the same email on two devices.

Advantages

  • Saves valuable space on the Server
  • Although unlikely, if your server crashes or terminate your hosting account, you will lose all your emails

Disadvantages

  • If you misplace or change your device, you will not have any record of the emails you sent.
    Additionally, if your mailbox is configured to delete received emails (Inbox items), you will also lose all your Inbox items if you lose or change your device.
  • If you have configured the email on multiple devices, you basically have many copies of the same email.

IMAP

IMAP actually stores the emails on the server and temporarily downloads the emails on your device. So the Inbox, Sent and other folders you see on your devices are actually the same as the server. So if you send an email from a computer, that sent email will be stored on the “Sent” folder on the server, which will also be visible on your smartphone or other device. Also, if you read an email on a certain device, that email will be shown as “Read” on the server and other devices

Advantages

  • Since the emails are stored on the server, you will not lose anything if you change or misplace your device
  • The same copies of emails on difference devices

Disadvantages

  • Although unlikely, if your server crashes or lose your hosting account, you will lose all your emails
  • Since emails are stored on the server, they need to be downloaded to be viewed. But the size of emails is usually small, so it shouldn’t be a problem.

Recommendation

For greater functionality and ease of use, IMAP is recommended.