Tony Finch writes:
On Fri, 25 Apr 2008, Paul Smith wrote:
The envelope sender for automated mail just be blank. That's defined
as the address you use if you don't want a bounce.
A null return path should not be used on a message unless it conforms
to one of a few standards-track types. RFC 2821 section 4.5.5.
2821 4.5.5 lists some types for which you should use the null path. It
doesn't forbid using <> for types not on its list.
3461 5.2.2 (d), 3834 3.3 and 5230 5.1 add to the list, and I would not
be surprised if other RFCs add more and code does even more.
Arnt