Honestly for vB 2.3.5, I have no idea. I've successfully banned that same domain (@cashette.com) using vs 3.6.4. You might want to try asking the guys over at vbulletin.com. Sorry.
eta: Absolutely, no idea if this will work for your board version, but you might want to use a hack like this one. I have it in place and it's Fantastic!
https://vborg.vbsupport.ru/showthread.php?t=131568