I am trying to switch the mail server settings under plesk to the following.

Names for POP3/IMAP mail accounts

It use to have this selected...

"Use of short (webmaster) and full (webmaster@domain.com) POP3/IMAP mail account names is allowed"

But now it has this selected ....

"Only use of full POP3/IMAP mail accounts names is allowed"

I tried to switch it back but it gives me an error stating that email names and passwords match. Question: Is there a way to scan the list to find out who matches?