I have just been looking at a problem with one of our
departmental mail hubs which is running qmail. The problem
was as follows:
The qmail host was sending mail to an internal address,
user@???
mail.cfs.le.ac.uk was a CNAME for sumac.cfs.le.ac.uk, so
qmail was rewriting the envelope recipient to user@???
But, sumac.cfs is an Exchange server, and could not be made
to accept mail for sumac.cfs; for reasons not entirely clear
to me, it would only recognise user@???
We have solved the problem by making mail.cfs an MX record,
pointing to sumac.cfs, so that now qmail will not rewrite
the addresses.
Nothing to do with exim so far, you might think...
But, it made me wonder how my exim mailhubs have been sending
mail to user@??? for the last N months, with
no trouble at all. It would appear that exim does not
canonicalize domains in addresses when it finds a CNAME.
Is this true? If so, why is it so, when RFC 1123 states:
5.2.2 Canonicalization: RFC-821 Section 3.1
The domain names that a Sender-SMTP sends in MAIL and RCPT
commands MUST have been "canonicalized," i.e., they must be
fully-qualified principal names or domain literals, not
nicknames or domain abbreviations. A canonicalized name either
identifies a host directly or is an MX name; it cannot be a
CNAME.
I'm not saying that I think exim *should* do this - I don't
see a good reason for messing about with recipient addresses.
I'd just like to know why exim ignores this (if it indeed does).
I could not find any discussion of this in the docs.
Thanks for reading...
Craig
___________________________________________________________
Dr C Foster cf2@???
Systems Management 0116 252 2245
University of Leicester Computer Centre Leicester LE1 7RH
