RDNS Issues

[rednik]

Can any of you Guru's help with what is probably a simple problem.

Our company uses a single mail server to send mail from several domain names.

The server has a single address on the web, and a RDNS against this address returns just one of the domain names which is sending mail.

As more people are using RDNS lookups to verify the originating mail server in an attempt to block spam we are finding that mail from the other domain names is getting blocked.

Is there a way I can assign multiple domains names to an IP when a RDNS is run against it?

Thanks

 

[FaiTHLeSS]

You would assign it the same way you assign the 1st rdns, but when someone does a lookup it doesnt mean they are going to get the right answer you want them to have.

It shouldnt matter what your rdns is for your mail server as long as you have one.

As long as your PTR records have matching A records the mail should pass through fine. If they records didnt match it could show up as forged mail.

 

[ChrisAC]

What you can do is point all the MX records for your domains at one host and then point the PTR at that.

eg

firstdomain.com IN MX mail.firstdomain.com
mail.firstdomain.com IN A 11.22.33.44

then for the other domains ..

seconddomain.com IN MX mail.firstdomain.com

thirddomain.com IN MX mail.firstdomain.com

forthdomain.com IN MX mail.firstdomain.com

Then in the 33.22.11.in-addr.arpa zone you can just have one PTR ..

44.33.22.11.in-addr-arpa IN PTR mail.firstdomain.com

So, it doesn't matter what domain you send from as the remote mail server checks DNS against the IP adress of the sending mail server, not the "mail from" address. It will see a connection from 11.22.33.44 and then do an RDNS lookup which will map to mail.firstdomain.com. If it then looks up mail.firstdomain.com it will find that it resolves to the same address.

Chris.

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Chris Andrew, CCNA, CCSA
chris@iproute.co.uk
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