[Exim] CNAME and recipient rewriting

Hello,

I see that exim doesn't rewrite the envelope recipient when it finds a
CNAME record for the domain part. Qmail does that and I'm told by a
qmail user that it's written in rfc2821 that CNAMEs should be handled
that way. I read the rfc and couldn't find anything that would suggest
rewriting. Would pls someone that knows SMTP and its standards better,
clarify this?

-m-