[Mimedefang] Domain canonifyin​g and RFCs

Marcus Schopen lists at localguru.de
Sat Sep 24 17:50:26 EDT 2016

Am Donnerstag, den 13.10.2011, 10:57 +0200 schrieb Ernst du Plooy:
> I posted the following on the sendmail (comp.mail.sendmail) newsgroup,
> but I don't get any reaction.  I realise this is not a mimedefang
> problem, but I'm sure some of you have also run into this issue.
> RFC 821 section 3.7 states "Whenever domain names are used in SMTP
> only the official names are used, the use of nicknames or aliases is
> not allowed.".  This however changed in RFC 2821 section 3.6 where is
> states that CNAME RRs may be used.
> Currently Sendmail still rewrites the sender domain.  Does this mean
> that the default behaviour of Sendmail is not RFC compliant or are
> there other RFCs that still limits the use of CNAMEs with MX records
> (maybe RFC 1034 section 3.6.2)?
> Thanks
> P.S.  I know the setting confDONT_EXPAND_CNAMES will disable this
> behaviour, but I would prefer not to implement this.  Also I cannot
> modify the DNS records since it is an external DNS server.
> They insist their DNS settings are RFC compliant.
> Their DNS records looks like this:
> c.domain.com      IN      A
> a.b.domain.com.  IN      CNAME   c.domain.com.
> c.domain.com.    IN      MX      10   mail.domain2.com
> c.domain.com.    IN      MX      20   mail2.domain2.com
> user at a.b.domain.com will be rewitten to user at c.domain.com

Old thread, but I ran into the same problem on Ubuntu 14.04 LTS
(sendmail 8.14.4) today. Setting confDONT_EXPAND_CNAMES to True fixed
it. Shouldn't that be put to default sendmail.mc? Took me three beer to
figure out the problem, because I never looked into that dark corner.


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