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I'm setting up my first e-mail server (Gentoo Linux w/postfix). The server is a self-managed box I rent from a company that sells rack space. But my name servers and registration are provided by another company.
Anyway, I'm going through an old copy of "The Book of Postfix" and trying to make sure my DNS configuration is all correct. The book says that my A RECORD should match my PTR RECORD, or there could be problems communicating with some e-mail servers.
I can dig my server's fqdn just fine, which is in the domain I bought from the company that handles the registration. However, if I dig -x to do the reverse lookup for the ip address, instead of that fqdn, I get an internal fqdn made up by the company that is taking care of my self-managed computer.
/As far as I know/ this hasn't caused any problems sending or receiving e-mail. But is this an issue that will need to be resolved? And if so, who should I be talking to? (My name server provider or my rack-space provider?)
It should be resolved, yes, because if your forward and reverse DNS do not match your server will be trusted less (the non-matching is typical of cheap or home setups). I believe you need to talk to the company that is taking care of your self-managed computer.
My ISP will allow you to change the reverse DNS if you are a business grade customers with static IP addresses but residential customers are stuck with the default naming. If you are running a mail server on a residential account, one way around a lot of problems is to relay your mail through your ISP's SMTP server. Mail still originated and is received by your server (BTW, it doesn't show as being from your ISP domain) it is just that their SMTP becomes the first hop along the path rather than directly on to the Internet.
If the server only handles incomming mail then this shouldn't be a big problem.
Like AlucardZero stated, the reverse lookup is used to see if your server can be "trusted" and sometimes this configuration needs to be accurate to get your IP cleared from blacklists, but this doesn't mean that no other servers will not trust your server at all!
If I am not mistaken, spam software will compare the ptr and the mx record to see if the server they are receiving mail from can be trusted, if they don't match the mail is subject to get a higher score.
ptr records are handled by the ISP, so in this case the company where you are renting the server/rackspace.