Hi all,

We have servers using a common gateway on a public IP.

We have SMTP running behind it and so sending emails. But we are receiving some SMTP errors as the SMTP server receiving the email is not able to successfully do a reverse DNS on the IP. This is normal as no PTR record is not configured.

So my first reaction was to say: send an email to your ISP, and ask him to create a PTR record for me.

BUT as it is the gateway of our network, I was thinking that we maybe need to use this IP for different services and therefore, we would have:

193.9.0.74 -> smtp.mydomain.com
193.9.0.74 -> gateway.mydomain.com

And this will start to do DNS round robin for the reverse lookup.

This means that when the SMTP server will receive the request, it will receive once smtp.mydomain.com then gateway.mydomain.com

My question is:

Will the SMTP server of the recipient freak out and consider my email server as a spam server as the reverse lookup will have 2 different FQDN?


I hope I have been clear enough. If you need anymore explanation please let me know.

Thanks in advance for your time to answer!

Gael

well you'd only have one PTR normally. I find that it's best to match up one A and one PTR to one IP. This record is the name of the MACHINE, and then have CNAME records pointing to the A for the aliased names, the names of the SERVICES and such like. Note that it's pretty chuffing common for a single SMTP server to accept many many domains. My personal domain is MX'd by google (boo hiss...) and they only have PTR records to their own google machine name of course.

Thanks Chris.

Let's go a bit further with some question regarding SMTP.

When I am sending an email, the hostname of the email will be mysmtpserver.mydomain.com (the one I configured in exim).
Then say, that the PTR for the public IP of the server is the gateway, therefore shared by several machines and the PTR record is gateway.mydomain.com

When the destination SMTP server will say 'HELO' it will first do it with mysmtpserver.mydomain.com then the SMTP server will do a reverse DNS query on the incoming public IP and see that it returns gateway.mydomain.com which is different from mysmtpserver.mydomain.com

What will happen in this case? Would I be blacklisted or would I receive some bounce messages? Or would it be OK?

Please let me know.

Thanks a lot in advance!

Gael

Ok so after calling the ISP where it was failing, they all said that they are only interested in having a response from the reverse DNS query.

So it does not matter if the hostname and the answer of the reverse DNS query are different.

Obviously, do not take that as the gospel and double check with the ISP to make sure it is fine with them...

HTH.
Gael