Re: [9fans] rewriting From:

[Gabriel Diaz Lopez de la Llave <gabidiaz@ipsoluciones.com>]

Hello,


I hope the following lines have some utility:

RFC-821 says that CNAME is supposed to be rewritten but

RFC-1123 says:

 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 take a look to rfc 2476 "message submission" and says

"
8.7.  Resolve Aliases

   The MSA MAY resolve aliases (CNAME records) for domain names, in the
   envelope and optionally in address fields of the header, subject to
   local policy.

   NOTE:  Unconditionally resolving aliases could be harmful.  For
   example, if www.example.net and ftp.example.net are both aliases for
   mail.example.net, rewriting them could lose useful information.

8.8.  Header Rewriting

   The MSA MAY rewrite local parts and/or domains, in the envelope and
   optionally in address fields of the header, according to local
   policy.  For example, a site may prefer to rewrite 'JRU' as '
   J.Random.User' in order to hide logon names, and/or to rewrite '
   squeeky.sales.example.net' as 'zyx.example.net' to hide machine names
   and make it easier to move users.

   However, only addresses, local-parts, or domains which match specific
   local MSA configuration settings should be altered.  It would be very
   dangerous for the MSA to apply data-independent rewriting rules, such
   as always deleting the first element of a domain name.  So, for
   example, a rule which strips the left-most element of the domain if
   the complete domain matches '*.foo.example.net' would be acceptable

"
On Thu, 2003-04-03 at 18:03, David Presotto wrote:
> I've noticed over the years that if the domain name in a From: address has
> a CNAME, then it gets rewritten by most sendmails.  Anyone know if there
> is an RFC that covers the subject?
>

Gabriel
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