Last updated: 28/7/2017
POP3 (Post Office Protocol 3) and IMAP (Internet Message Access Protocol) are the two main protocols used by applications to send and receive email. You can find out the differences between the two and which is best for your needs in the following article: What are the differences between POP3 and IMAP?
Should you decide you wish to change your email account from using a POP3 connection to an IMAP connection in Apple Mail, you can do so using the following steps.
Switching from a POP3 connection to IMAP can result in your existing email being deleted, so you should create a backup of your mailboxes to avoid losing anything important.
With the backup completed, you can now delete the POP account in Apple Mail. You should also delete the account on other devices you use for email.
If you are asked to confirm the port configuration, use the following details:
You can view your port settings in Apple Mail by selecting Mail > Preferences from the Menu bar. Select your account from the sidebar of the panel that opens, then click the Server Settings tab. If you wish to change the preconfigured port settings, uncheck the Automatically manage connection settings option for both the Incoming Mail Server (IMAP) and Outgoing Mail Server (SMTP) sections. You can now edit the port configuration.
If you wish to restore the mailboxes and email you backed up earlier...