...
Change Authentication to Password
- Open Mail.
- Go to Preferences > Accounts > Advanced Preferences > Accounts > Advanced and select your IMAP account IMAP account account in the left-hand side.
- Find and check the Use SSL Use SSL box box. The port should automatically set to 993.
- Under Authentication, change it to Password.
- Save, quit and restart Mail.app.
- If requested, enter your password again and check "Remember my password in my keychain." "Remember my password in my keychain."
...