Wietse Venema wrote: >> Hi list, >> >> I saw this in my logs: >> >> Apr 29 14:58:08 mx postfix/smtpd[4880]: connect from >> xxx.yyy.zzz[xxx.yyy.zzz.xxx] >> Apr 29 14:58:09 mx postfix/smtpd[4880]: warning: valid_hostname: empty >> hostname >> Apr 29 14:58:09 mx postfix/smtpd[4880]: warning: malformed domain name >> in resource data of MX record for somedomain.com: > > There is no Internet RFC that says that an empty hostname is valid. > Postfix was not built by experimentation of "what works". Instead, > Postfix was built by looking at official email standards. Then, I > added hacks and workarounds for systems that don't play by the > rules. > >> Apr 29 14:58:09 mx postfix/smtpd[4880]: NOQUEUE: reject: RCPT from >> xxx.yyy.zzz[xxx.yyy.zzz.xxx]: 450 4.1.8 <i...@somedomain.com>: Sender >> address rejected: Malformed DNS server reply; from=<i...@somedomain.com> >> to=<u...@example.com> proto=ESMTP helo=<xxx.yyy.zzz> >> Apr 29 14:58:09 mx postfix/smtpd[4880]: disconnect from >> fxxx.yyy.zzz[xxx.yyy.zzz.xxx] >> >> And: >> >> $ host somedomain.com >> somedomain.com has address yyy.zzz.xxx.yyy >> somedomain.com mail is handled by 0 . >> >> This looks like a Null MX record: >> http://tools.ietf.org/html/draft-delany-nullmx-00 >> >> If the domain owner declares that this domain never sends or recieves >> email, then shouldn't postfix reject the above message with a permanent >> error? > > Anyone can post a draft. That does not mean that they change > the rules of the Internet. > > The SMTP RFC says that the MX record specifies a hostname, and > there is no RFC that says an empty string is a valid hostname. > > The warning message is an example of a workaround hack that I put > in for systems that don't supply valid hostnames in their MX records. > > Wietse
Hi Wietse, I understand. Thank you for clarifying this. I was not aware of the ugliness in this method. It seemed like a quite easy way to implement non-email domains for a DNS admin, but I now understand what complications this brings to the application developer. Cheers, Mikael Bak
