[Mimedefang] non-multipart eml blocking ?

[Charles Mount]

The non-multipart .eml blocking rule (straight from
mimedefang-filter.example) is blocking almost everything we get from one
small company.   They are using Lotus Notes.  This rule is blocking very
little from anyone else.

What is the risk of disabling this rule and what can the sending company do
to avoid this problem???    Our inbound mail is virus scanned several times
along its path to the user.