On Wed, 2009-09-09 at 11:01 +0100, Jonathan Gilpin wrote: > Surely I need to prevent this from being allowed? How can I make Exim
> reject a message if MAIL FROM: is blank?
You can't (well, you can, but you must not). "MAIL FROM:<>" is the
universally accepted indicator of an NDR or other type of bounce.
It's also used all over the world as the envelope sender for Out Of
Office messages (well, it should be, but all too often isn't).
Acquaint yourself with RFC5321 to see where acceptance of such messages
is mandated.
