[exim] Refusing MAIL FROM:<> ...

Hej,

exim with address callouts says "Refusing MAIL FROM:<> does not help
fight spam, disregards RFC requirements, and stops you from receiving
standard bounce messages." if a host does not accept the "MAIL FROM:<>"
command. Despite being correct on the spam and bounce message part, I'd
be interested in which RFC requirements exactly were "disregarded". I
couldn't find any references in RFC 2821 at least.

Oh, one second thing:
Exim also said: "(result of an earlier callout reused)". But RFC 2821
says (section 4.5.4.1, Par. 9): "More significantly, 5yz responses to
the MAIL command MUST NOT be cached.". Hmmm.


lg,
daniel