It used to work just fine before I enabled two factor authentication. I have since disabled two factor authentication but I can still not authenticate with IMAP.

So here's what's happened:

1. Enabled two factor authentication and changed password.

2. At this point, IMAP authentication starts to fail, this is expected.

3. Generated app password for IMAP.

4. Enter it a thousand times correctly into the client, without spaces, with correct case.

5. Still no authentication. Clients complain that credentials are invalid.

6. Verified that all server settings are correct.

7. Regenerate app password.

8. Enter new password to client a thousand times.

9. Still no authentication.

10. Tried entering the account password into client instead of app password.

11. Still no authentiation.

12. Disabled two factor authentication.

13. Enter account password into clients.

14. Still no authentication.

At this point my account is unusable. Thanks Zoho.