On Tue, Jul 14, 2009 at 3:41 PM, Daniel L'Hommedieu <dlhommed...@gmail.com> wrote: > > On Jul 14, 2009, at 15:32, Scott Haneda wrote: > >> On Jul 14, 2009, at 12:06 PM, Tim Legg wrote: >> >>> ;; ANSWER SECTION: >>> timothylegg.com. 9220 IN MX 10 mail.timothylegg.com. >>> >>> >>> My hostname is genex.timothylegg.com on my machine and my MX record points >>> to mail.timothylegg.com >>> >>> I was wondering if the MX record should point to the same name as my >>> hostname. Obviously, this isn't too big of a problem, since my mail works >>> after all. I don't know if this something that I should have corrected or >>> if is it standard as it is? >> >> >> The MX should point to an A record that resolves to the IP address that >> postfix listens on. I believe that is the only requirement. My postfix >> server will use the hostname of the ehlo/helo in a transaction, which is not >> the same as my MX, and has never caused me any trouble. >> >> I believe your setup is perfectly reasonable, and should work fine. > > My server runs on a dynamic IP address on a cable modem, and I use dyndns.org > to get to it from remote. The machine's hostname matches the name in the MX > record, but the host record in DNS is a CNAME record, not an A record. The > CNAME points to a dyndns.org hostname, which does have an A record (which is > updated by a dyndns client running on my server). I have run things this way > for a long while with no issue. "A long while" is: years on sendmail, and > months on postfix.
RFC 2181 Clarifications to the DNS Specification July 1997 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. > > Daniel
