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  1. James Server
  2. JAMES-441

Add an option to support aliases (CNAME) for MX records

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    • Improvement
    • Status: Closed
    • Major
    • Resolution: Fixed
    • 2.2.0
    • 2.3.0
    • DNSServer
    • None


      rfc2181 ((Clarifications to the DNS Specification) clearly explain that this should not be done:

      10.3. MX and NS records

      The domain name used as the value of a NS resource record, or part of
      the value of a MX resource record must not be an alias. Not only is
      the specification clear on this point, but using an alias in either
      of these positions neither works as well as might be hoped, nor well
      fulfills the ambition that may have led to this approach. This
      domain name must have as its value one or more address records.
      Currently those will be A records, however in the future other record
      types giving addressing information may be acceptable. It can also
      have other RRs, but never a CNAME RR.

      Searching for either NS or MX records causes "additional section
      processing" in which address records associated with the value of the
      record sought are appended to the answer. This helps avoid needless
      extra queries that are easily anticipated when the first was made.

      Additional section processing does not include CNAME records, let
      alone the address records that may be associated with the canonical
      name derived from the alias. Thus, if an alias is used as the value
      of an NS or MX record, no address will be returned with the NS or MX
      value. This can cause extra queries, and extra network burden, on
      every query. It is trivial for the DNS administrator to avoid this
      by resolving the alias and placing the canonical name directly in the
      affected record just once when it is updated or installed. In some
      particular hard cases the lack of the additional section address
      records in the results of a NS lookup can cause the request to fail.

      But having Sendmail, postfix, qmail, and exim, around that support the aliased MXs simply let the sysadmin to not follow the RFC because "most" mta support the "trick".

      This article is related:



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            bago Stefano Bagnara
            bago Stefano Bagnara
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