Re: Undesirable address rewriting by ZMailer (Resend)

[Matti Aarnio <mea@nic.funet.fi>]

On Wed, Jul 28, 2004 at 01:20:07PM +0000, Ambrose LI wrote:
> [Sorry if this is a duplicate; for some reason I think
> my original mail didn't get sent properly to the list.]
> 
> Hello,
> 
> in ZMailer 2.99.56, it seems that when we mail to
> 
>    foo@example.com
> 
> where the "host example.com" looks like
> 
>    example.com is an alias for www.example.com.
>    www.example.com has address 10.11.12.13
> 
>    (i.e., instead of an MX or A record as expected,
>    they have a CNAME instead)
> 
> then ZMailer will silently rewrite the envelope
> address as
> 
>    foo@www.example.com
> 
> In some cases, this will cause example.com's mailer
> to reject the mail because www.example.com is not
> configured to receive mail.
> 
> Is this a known behaviour, and is there a way to
> disable it? Thanks very much in advance.

That stems from RFC 1123 section 5.2.2:

      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.

Revised form of it, the RFC 2821, does not say exactly.
The outgoing smtp transport agent does rewrite CNAME mapped
domain to its base form for RCPT TO, but does not touch on
MAIL FROM.

> Best regards,
> Ambrose
> -- 
> Ambrose LI Cheuk-Wing  <a.c.li@ieee.org>
> http://ada.dhs.org/~acli/
-- 
/Matti Aarnio	<mea@nic.funet.fi>
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