[AccessD] mdb block even though it was in a zip file

Dear List:
 
Client tried to send their back end zipped but in the zip file was a text
file with the text: "The file "AppareoMRP.mdb" has been blocked by the
attachment filter recipient policy on the %ANTIVIRUSENGINE% system.  The
email has not been delivered."
 
I don't think that Outlook did that on my end.  Could it have happened on
their?  Any clue what this means?
 
TIA
 
Rocky