Working on this now guys, so far cant see anything on the mail server to suggest anything, so i dont think there has been an intrusion at that level.

vB - The forum software is up to date in terms of "security" but there is an update I can install (vbulletin-4-2-5), I cant find much info on what this fix's or introduces but I do know it will probably just be code changes to support PHP 7+...

Just gonna look at these headers now, will report back.