Mac Mail: switching from POP to IMAP
Here is how you can proceed to switch to use IMAP on your Mac:
1- The first thing is to disable the POP account:
In Mail, choose Preferences -> Accounts, click on the name of your POP
account, then on Advanced, then uncheck Enable this account.
2- Set up a new account foryour email address on your new Mac Mail App,
selecting type: IMAP. Important: Make sure to name it differently than
the old one using POP.
3- Once that one is set up, check your email with the IMAP account and let it sync mail with
the server for a while (it can take a few minutes to a few hours depending of your mailbox size).
4- Once the new IMAP account is finished syncing:
Test you can send and receive email.
5- After that you could delete the old (POP) account from the Mail application
or choose to keep as a mail archive for the old mail that has been downloaded to your computer.