POP3 stands for Post Office Protocol version 3. It uses TCP Port 110.
POP3 provides a way to receive emails from an email server.
POP3 has been around for a long time. It’s used to retrieve email messages from the Internet server provider. It then downloads the mail to the local mail client. You can then have the option to delete the mail from the server once it’s been downloaded. This process of deleting the email from the server only made sense if you only had 1 device that was downloading the mail. Nowadays we can have multiple devices collecting email, so deleting the email from the server once it’s downloaded to one device doesn’t make sense.
Legacy equipment may still use POP3.