POP3 and IMAP are two different protocols used to access email.
When you need to check your emails from multiple devices such as a work laptop, a home computer or tablet, smartphone or other mobile device.
Tap into your synced (updated) account from any device with IMAP.
POP3 downloads email from a server to single computer then deletes it from the server.
Because your message get downloaded to a single computer or device and then deleted from the server.
It can appear that mail is missing or disappearing from your inbox if you try to check your mail from a different computer.
In POP3 can use only one computer to check your email.
IMAP can use multiple computers and device to check your email.