msn email occasionally removes email attach;ments

When I receive an email with an attachment, sometimes (about 10 % of t;he time).,  I get a note on the email, under attachment, that th;e attac;hment was not reviewed for viruses, and th;e attach;ment was removed from the received email.  Therefore it would not open, and the email has no value.  The attachment is vital to the pupose of why t;he emai was sentl.