There is not reason why I can think of that the person can't open your back
end mdb file.

they do have to use a full standard (and legal) path name to that back end.
That means the persons web server must be able to BROWSE TO THE FOLDER WHERE
THE back end mdb file resides.

In other words, the connection to the back end is a standard file share.
You can't use a  socket connection (ip address) *over* the internet to do
this, you must use windows networking.

Other then the above, I don't see why the file can't be opened. I assume
that the back end file is placed on the web server?