Right-click on the IMAP account and click on Settings… Now you’ll want to remove your IMAP account from Thunderbird to ensure that it doesn’t keep trying to make a duplicate connection to the server, since your POP3 account is already going to connect and retrieve your email.Now if you login to webmail, you’ll see all those messages have been removed from the server. You can select one of the messages from your IMAP account, then hit Ctrl-A to select all messages, then drag them into your POP3 account to move these messages off the server.If you attempt to login to webmail at this point, you’ll see these same messages stored there. At this point you can now see that our original IMAP account has 5 messages in it, and these are stored on the server.Now back on the Account Settings window, click on the newly created account, and update the Account Name to append (POP3) on the end, so we know which account is which easily, then click OK.Now select POP3 (keep mail on your computer) and click Done.
If you’re having IMAP resource usage problems switching an IMAP account to POP3 is a great solution!
