Post Office Protocol version 3 refers to the POP3 protocol which is used to download emails from an email account or server to your local email device.

The POP3 setup downloads emails from an email server to the device you are using to access the email account, sometimes deleting the emails from the remote email server once they have been downloaded.

By using POP3 to access your emails, if you are using multiple devices, the reading, replying or deletion of emails will not be shown on other devices accessing the same email account.

Since POP3 downloads emails to your local device, email changes will not be synchronised across other devices. Losing or damaging the device which is being used to access emails using POP3 may also mean the loss of your emails.