SOL on rDNS?

March 2, 2008 12:38 PM

My company can't send messages to some larger ISPs due to reverse DNS not being setup. But we're in a situation that isn't so easy to solve...

My company leases space in a building. The company shares a single public IP with all the other businesses. Over the last couple of years, it's become increasingly more important to make sure that reverse DNS is set up properly in order to send email over the Internet, especially to large ISPs like ATT.

Since all the companies share a single public IP, I believe that a simple call to the ISP that services the building will not work here we would, in essence, be usurping any of the other IP-sharinf companies ability to set up reverse IP for themselves.

So, what are we to do? If we can't setup reverse DNS this way, is there another way to do it so we can get around this increasingly necessary requirement?

For what it's worth, we run a Windows server.

posted by tcv to technology (11 comments total)

Wouldn't the reverse DNS have to be set up by the owner of the block of IPs? You should just ask the ISP who provides the connection to set up reverse DNS (e.g. probably a third-level hostname under the ISP's domain name). I don't think there's anything you can do to create reverse DNS for your IP address unless you're somehow already the authoritative DNS for it (very unlikely if you have only one IP).
posted by winston at 12:45 PM on March 2

In general, what *most* mail senders are looking for is that your IP be RDNSed to something that does not look like a dialup block, and that what it reverses to is then valid as a forward lookup for the same name.

The extra level some mail admins go to, which will indeed screw all of you, is requiring that those two lookups also match the HELO from your mail server.

Can't do that with multiple servers...
posted by baylink at 1:06 PM on March 2

First, talk to the engineers at your ISP, and see if they have a good solution. This is the kind of problem that business-grade service should be able to solve.

If that fails, use an external provider to host mail.yourdomain.com with a SMTP server... with a bit of hacking, you should be able to get that mail relayed back to your normal server, and it's a relavitvely simple service that shouldn't be too expensive.
posted by qxntpqbbbqxl at 1:08 PM on March 2

qxntpqbbbqxl, I'd been wondering if an external service might help. Perhaps a smarthost? Any thoughts on who?
posted by tcv at 1:20 PM on March 2

If you're interested in outsourcing your email, what would be the requirements? Personally I think Google Apps for Domains is the best thing ever.
posted by winston at 1:22 PM on March 2

Send your email via an external email server.

There's no shortage of companies offering such services. Try and find a clueful bunch though.

Phil
posted by pharm at 1:30 PM on March 2

I'd contact the ISP and see if they will set up a smarthost for you. They may offer this (AT&T does for DSL customers). Alternately, see if the ISP will let your client (Outlook) send directly using SMTP credentials (which is the same thing as a smarthost, just not on the mail server).
posted by disclaimer at 3:29 PM on March 2

Seems like I could also do smarthost via mailhop.
posted by tcv at 5:05 PM on March 2

Okay, you're talking about the broadband provider supplying one static IP # for all the companies that are in the building. Your domain may or may not be hosted by this ISP.

One question you didn't answer is how are all these companies in the building receiving mail if there's only one shared static IP #? Your question presumes that there must be multiple mail servers in the building for your reverse DNS issue to be a problem.

A typical broadband setup maps a port, like POP mail port 110, to a particular internal LAN address so all POP mail connections to the external IP # gets routed automagically to the internal IP address of the mail server.

If you've got a bunch of companies using one static public IP #, and presumably some of these companies are sending and receiving mail, that would be impossible to do as you can only map one port # to one internal address.

So, I would think that your description of the building network must be inaccurate or there would be a way to set up reverse DNS if you are receiving mail along with other companies via standard POP protocol.

Mailhop is a good suggestion for resolving the issue regardless.
posted by diode at 9:12 PM on March 2

There seems to be some confusion with some answers. I take it that there is no problem receiving mail, just sending.

I've setup some mail systems recently and most servers that care about reverse IP are checking that the IP of your server has a reverse IP name and that that name resolves in the forward direction back to the same IP. The fact that multiple domains send from the same IP doesn't matter. I haven't found one yet which strictly enforces the HELO name. winston is correct. The owner of the IP block (probably the ISP) needs to setup the reverse IP. The name they choose doesn't really matter to you.

If that turns out to be too difficult then the SmartHost host suggestion is good. Again, if the ISP doesn't make this easy then get yourself an account at a web host which also offers mail.

I look after the IT needs of a school where we have an outgoing mail server on a DSL line. Our server is configured to send all mail to a mail server at JodoHost where we have a low cost account so they can relay for us. The recipient's server sees the mail coming from JodoHost so they are happy.
posted by tetranz at 5:02 AM on March 3

Well, maybe it's best just to talk to XO and see if there's anything we can do there. Otherwise, yeah, we'll probably do some kind of smarthost.
posted by tcv at 4:21 PM on March 3