Emails deleted with reason "Block user list"

Hello 

Sophos email has begun suddenly to delete emails from a particular sender to a particular recipient , as the user set with "block sender" this behavior,

but he told me that it hasn't set anything to cause this.

Is there a way to see individual "user block" lists or to understand what's going on ? 

I opened a case to support but is't still unresolved....

Thanks 

Regards 

Antonello