Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

We have an SMTP server setup on an internal IP (10.x.x.x) that will send email to our customers. Since the server is inaccessible to DNS lookups from the outside, will this cause issues for sending and/or NDR's? I also told them to set up and SPF record for the domain, but since the server is not public, I doubt it would do any good.


share|improve this question
up vote 6 down vote accepted

If the server has no way of contacting the outside world, then yes this will be a major problem. If you're using NAT, then the server will appear to be connecting from the NAT's external IP.

If you do not have forward and reverse DNS configured properly then many servers will not accept e-mail from your server. If you're server announces itself as then DNS must resolve to the NAT's IP address. Also, the IP's reverse pointer must point to (eg, if your external IP is then must be a PTR to

SPF records match DNS Host names usually (though you can include IPs, it's not a best practice). SPF records have to be somewhat carefully crafted or else they'll work against you; do take a bit of care in setting one up and it will greatly reduce the number of your outgoing e-mails that end up in people's Junk bins.

share|improve this answer
Was typing up the same - beat me to it by 30 secs! – Robin Gill Feb 28 '12 at 14:04
Gotta get something 'good enough' and post it, then go back a fill in the details. =] – Chris S Feb 28 '12 at 14:05
It can contact the outside world. It's hostname is set up as ics.local. It seems to announce itself as for whatever reason. That is not even a domain of ours. We are using MailEnable and I don't have direct access to check if that is something they put in because ics.local is not a valid tld. Here is some of the log info EHLO 250-Postini says hello back 14 67 MAIL FROM:<> 250 Ok 14 8 RCPT TO:<> 250 Ok 34 8 – KrunchMuffin Feb 28 '12 at 14:21
You should be able to configure what the mail server software announces itself as. I'm not familiar with that software, but the configuration option is usually something like "HELO Name", "Masquerade Name", or "Server Name" – Chris S Feb 28 '12 at 14:24
So just so I can get back to them with correct information, we will have issues with sending emails to some domains by not having an rDNS set up? – KrunchMuffin Feb 28 '12 at 14:47

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.