Emails quarantined with no attachment.

We are occasionally getting emails quarantined for reason MIME type is executable file type attachment. The issue appears to be intermittent and probably depends on some trick of the actual email contents.

There is actually no EXE type attachment of any kind, and often no attachment.

This only seems to happen to Cyrillic language emails between Russian staff.

It is annoying as IT has to manually release them. Any ideas?