BTW, you really MUST NOT point your MX record(s) at CNAMEs:
$ host -v -t mx mailnewsrss.com
Query about mailnewsrss.com for record types MX
The following answer is not authoritative:
mailnewsrss.com IN MX 0 mail.mailnewsrss.com
*** mailnewsrss.com MX host mail.mailnewsrss.com is not canonical
The target domain of an MX record _MUST_ be a valid hostname.
At Mon, 23 Nov 2009 16:52:01 -0800, ML <mailingli...@mailnewsrss.com> wrote:
Subject: Multiple Mail domains for reverse ptr records? I'm confused
>
> I have some confusion about multiple reverse PTR records per IP.
>
> Comcast has told me that they can only assign 2 reverse PTR records per IP.
That 2-PTR restriction must be some limitation in Comcast's provisioning
software, or possibly some administrative limit they enforce to try to
make their customers adhere to some kind of usage policy.
The DNS protocol and design itself allows you to have as many PTRs as
will fit in a single DNS reply, though realistically most software will
only ever see at maximum 35 PTRs for a given address regardless of how
many are sent in the reply. (that's the default limit built into the
most commonly used DNS resolver code)
> So if I have mail.domainA.com and mail.domainB.com this is fine. If
> the reverse lookup is done and it is not correct, it will retry and
> get the second record and all is well.
You don't need to do that. You don't want to do that. It is not
scalable.
However if you do end up having more than one hostname pointing at the
same IP address then you _really_ do want to have a PTR for each of
those hostnames -- while it may be _sufficient_ for some software, such
as Postfix, to find just one valid PTR, the rationale for using reverse
DNS requires that PTRs and A RRs be 100% orthogonal in order for the
reverse DNS to be truly meaningful and useful.
One wants to be able to find _every_ valid hostname for a given IP when
one does a reverse DNS look-up -- anything less makes all the unmatched
hostnames look like they are invalid and bogus users of the IP address.
It is impossible to validate any unmatched hostname as a valid user of
an IP address. For example should some connection arrive from a client
and it gives as its name one which cannot be matched in the reverse DNS
then there is no way to know that it is a valid and authorised user of
the IP address it is connecting from -- it could be hijacking a
connection from the source network -- it could even be TCP spoofing its
source address (if other measures are not also protecting against TCP
spoofing).
Keep your forward and reverse DNS hostnames and PTRS 100% consistent.
Do it for the rest of us, if not for the sanity of your own IP address
assignment and bookkeeping.
One of your current hostnames is not valid in the current reverse DNS:
$ host -Av mailnewsrss.com
Query about mailnewsrss.com for record types A
Checking reverse mapping consistency for host mailnewsrss.com
Hostname mailnewsrss.com maps to address 173.13.167.209
Found 1 address for host mailnewsrss.com
Checking if address 173.13.167.209 has the hostname mailnewsrss.com
mailnewsrss.com address 173.13.167.209 maps to hostname mail.mailnewsrss.com
mailnewsrss.com address 173.13.167.209 maps to hostname
mail.theindiecompanyllc.com
*** Hostname mailnewsrss.com does not belong to address 173.13.167.209
*** Not all addresses for hostname mailnewsrss.com have a matching hostname.
> How do people then run a large mail server with many domains? I have
> about 10 domains that need e-mail and I wanted to build a single mail
> server to handle this. But now I guess it can't be done?
The normal sane way to host multiple domains on the same server is to
use MX records for each domain, all which point at _ONE_ hostname for
the mail server.
Proper use of MX records makes it possible for one mail server to handle
thousands and tens of thousands or even hundreds of thousands of domains
(depending on volume, of course). A single mail server instance, using
a single primary hostname, can recognise and accept messages for many
domain names.
Here's an example of multiple e-mail domains using one server:
mail.example.com. IN A 555.121.121.121
121.121.121.555.in-addr.arpa.com IN PTR mail.example.com.
cust-1-example.com. IN MX 0 mail.example.com.
cust-2-example.com. IN MX 0 mail.example.com.
cust-3-example.com. IN MX 0 mail.example.com.
[[ ... ]]
cust-n-example.com. IN MX 0 mail.example.com.
It is not necessary (or sane) for every domain used for e-mail to have a
unique hostname (i.e. "A" record) for the mail server which handles the
e-mail for that domain.
> What is my best way to accomplish this? I dont want a lot of machines
> cluttering up my apartment and consuming massive electricity until my
> startup is off the ground..
Why would you need more than one server? (assuming your one server and
your connection can adequately handle the traffic volume your users
cause to be directed at it, of course)
Even if you have multiple IP addresses, as well as multiple hostnames,
you can still host everything all on one server, if it has enough
capacity to handle the traffic load.
However you don't need multiple IP addresses, and you don't need
multiple servers.
--
Greg A. Woods
+1 416 218-0098 VE3TCP RoboHack <wo...@robohack.ca>
Planix, Inc. <wo...@planix.com> Secrets of the Weird <wo...@weird.com>
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