[Emailcore] Ticket #92: CNAME handling in “5.1. Locating the Target Host” (rfc5321bis)

[Alexey Melnikov <[e-mail]>]

Hi all,

In Section 5.1 I see the following text:

    The lookup first attempts to locate an MX record associated with the
    name. If a CNAME record is found, the resulting name is processed as
    if it were the initial name.

Is CNAME expansion only done once? Or multiple times? If
multiple times, what the minimal expected limit?

John Klensin suggested:

  RFC 1123 Section 5.2.2 prohibits CNAMEs in MAIL or RCPT
  commands. At some point we changed that and 2821 contains the
  text above, with no hints about iteration or recursion. I
  vaguely recall the change being made in some document between
  1123 and 2821, but that is a dozen or so very eventful years.

  I think being more specific requires involving the WG and
  recognizing that whatever we say is likely to render some
  existing implementation non-conforming. How would you feel
  about a statement in the A/S pointing out that long CNAME chains
  are a source of trouble, that, when possible, one should stick
  to 1123-style canonical names, and when that is not possible, to
  try to keep the chains short.

After thinking a bit more about this, I think I am happy with this proposal.
John, do you think I should just reassign this ticket to A/S or do you think some small clarification is needed in rfc5321bis?

Best Regards,
Alexey