Nothing that I can think of would completely block mail. Probably best to go straight to Technical Support, it's free by phone or online chat here: https://service.mcafee.com/
But probably best for that client to do it from the machine in question.
Ok, I have to go on the client or remotely access his computer to contact support.
OK good luck. That link is for Consumer product support by the way, not Enterprise, just to clarify.
Did by anyway stopped McAfee services and tested.
A.If McAfee stopped and issue resolved,please contact Tech support
B.If McAfee Stoped and issue not resolved.Please contact ISP/System manufacturer