IMAP only for virtual domain's default email account?

This is regarding the default user account, e.g. 'x', for the virtual host name e.g '' which has an email account named 'x -- unlike other email users under that host name, e.g. 'joe.x' for ''.

I found that I had to use IMAP to get authentication to work whereas other email accounts like 'joe.x' worked with POP.

Operating system Debian Linux 8
Webmin version 1.851
Usermin version 1.720
Virtualmin version 5.99
Theme version Authentic Theme 18.49-8
Time on system Tuesday, August 1, 2017 3:23 PM
Kernel and CPU Linux 4.9.36-x86_64-linode85 on x86_64
Processor information Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz, 1 cores


Howdy -- hmm, it shouldn't actually matter what protocol is being used, both should work similarly.

What error messages do you see in /var/log/mail.log and /var/log/auth.log when trying to log in as one of those users with POP3?