gmail addresses are banned when registering, but are *not* in the ban list
 

Re: vBulletin 3.8.4 PL2

I've had a number of reports from a site that gmail addresses are being rejected when new members try to register. The message they get is: Quote:
The administrator has banned your email address. You will need to change your email address in order to continue. If you think this is done in error, please click here to contact the administrator.

I've tested and found that any gmail address I try is rejected. Other email domains I tried are accepted. There are no gmail domains or addresses in the email ban list; there are no domains or addresses on the list that contain the 'gmail' string (i.e., loggmail.ru, etc.). I also disabled all plugins, and no change.

Any idea what's causing this and how to fix it?