Hi,
This question is not postfix-related .... so its somehow off-topic.
But it's related to mail systems, so i cant imagine any other place to
get some help on this subject.
I have a domain (domain.com.br) with lots of subdomains in the
format nnn.domain.com.br.
nnn.domain.com.br (about 40 different subdomains) have only 2 (two)
DNS entries:
nnn IN MX 10 server.nnn.domain.com.br.
nnn IN TXT "v=spf1 include:domain.com.br -all"
there's absolutely no A entries for the subdomains.
i'm having an isolated problem with a customer that cannot send
mails to one of my subdomains (everything else is working fine, several
thousand of messages flowing daily, this really seems to be an isolated
problem). Altough, their sysadmin (from the domain which cannot send us
mail) is telling what i'm doing (having an MX entry but no A entries) is
RFC-illegal, altough he cannot point me which RFC i'm not complaining with.
i really dont know if this setup (MX record but no A record) is
RFC-OK. The only think i know is that it's been working for years and i
receive thousand of emails daily on my several subdomains with no
problem at all.
question is .... do a domain (or in my case, a subdomain) *MUST*
have an A record ? Is the config i'm doing (DNS speaking) correct or
incorrect (RFC-speaking) ??
Thanks for any hints on that ....
Comments
Re: is this DNS setup RFC-correct ?
By mouss at 10/28/2010 - 15:34Le 25/10/2010 18:20, Leonardo Rodrigues a écrit :
to receive email, you need either an MX OR an A record. you do not need
both.
Obviously, Wietse has no problem receiving email:
$ host -t a porcupine.org
porcupine.org has no A record
$ host -t mx porcupine.org
porcupine.org mail is handled by 10 spike.porcupine.org.
$ host -t a spike.porcupine.org.
spike.porcupine.org has address 168.100.189.2
nor do I (for @ml.netoyen.net):
$ host -t a ml.netoyen.net
ml.netoyen.net has no A record
$ host -t mx ml.netoyen.net
ml.netoyen.net mail is handled by 10 tichka.netoyen.net.
$ host -t a tichka.netoyen.net
tichka.netoyen.net has address 91.121.33.217
while many domains have an A record, this is related to the web, not
smtp. it's just so that <a href="http://example.com/" title="http://example.com/">http://example.com/</a> works (for mobile devices,
"www." is 4 chars...).
Anyway, the "common" way to configure MX servers is
example.com. MX 10 joe.example.org.
joe.example.org. A 192.0.2.1
that is
- the domain has an MX record which is a "hostname"
- that hostname has an A record
Re: is this DNS setup RFC-correct ?
By Jeroen Geilman at 10/28/2010 - 15:40On 10/28/2010 09:34 PM, mouss wrote:
Um.
You just finished stating that it is.
If domain.com has an A record but no MX record, mail reception will work
just fine for <a href="mailto: ... at something dot domain.com"> ... at something dot domain.com</a> - as long as
something.domain.com is not delegated.
The web is unrelated to a domain having an A record.
Re: is this DNS setup RFC-correct ?
By mouss at 10/28/2010 - 16:10Le 28/10/2010 21:40, Jeroen Geilman a écrit :
let me restate what I meant:
google.com, aol.com, microsoft.com, ... have A records, and this is not
because of smtp.
This may mislead some people to believe that every domain must have an A
record.
Re: is this DNS setup RFC-correct ?
By Bastian Blank at 10/28/2010 - 11:24On Mon, Oct 25, 2010 at 02:20:51PM -0200, Leonardo Rodrigues wrote:
| ;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 65089
| ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
|
| ;; QUESTION SECTION:
| ;nnn.domain.com.br. IN ANY
Nope, nnn.domain.com.br does not exist at all.
It is. See RFC 821, 5321.
No. The name listed in the MX record may also only have AAAA for
example.
Bastian
Re: is this DNS setup RFC-correct ?
By Scott Lambert at 10/25/2010 - 17:44On Mon, Oct 25, 2010 at 02:20:51PM -0200, Leonardo Rodrigues wrote:
Does an A record exist for server.nnn.domain.com.br? If not, how
are we supposed to figure out where to actually direct mail for
<a href="mailto: ... at nnn dot domain.com.br"> ... at nnn dot domain.com.br</a>? If you don't have an A record for
server.nnn.domain.com.br, I believe you have a dangling MX record.
Is the MX record supposed to be ?:
nnn IN MX 10 server.domain.com.br.
Maybe I've missed something in your problem description. Some very
smart people have responded before me without mentioning this. I
probably missed something.
Re: is this DNS setup RFC-correct ?
By Christoph Anton... at 10/25/2010 - 13:41I know SPF is disliked here ;)
On Mon, 2010-10-25 at 14:20 -0200, Leonardo Rodrigues wrote:
Cheers,
Chris.
Re: is this DNS setup RFC-correct ?
By Jeroen Geilman at 10/25/2010 - 13:49On 10/25/2010 07:41 PM, Christoph Anton Mitterer wrote:
Like doesn't enter into it.
Discussion of SPF is verboten. simple.
Re: is this DNS setup RFC-correct ?
By Victor Duchovni at 10/25/2010 - 14:37The politics and wisdom of SPF are off topic. Simple configuration
questions relevant to Postfix, that touch on SPF, are not taboo.
DNS pedantry is also off topic. The vast majority of SPF deployments use
TXT records to publish SPF policy. This is not the forum for quixotic
campaigns to change the status quo.
Re: is this DNS setup RFC-correct ?
By Christoph Anton... at 10/25/2010 - 14:06On Mon, 2010-10-25 at 19:49 +0200, Jeroen Geilman wrote:
Cheers,
Chris.
Re: is this DNS setup RFC-correct ?
By Wietse Venema at 10/25/2010 - 12:36Leonardo Rodrigues:
The EMAIL RFC requirement is that a domain name has an MX record
or an A record (see RFC 5321 Section 5). There is no EMAIL RFC
requirement to have an MX record AND an A record.
Wietse