I recently brought an outsourced email back in-house and have had a few issues sending email only to certain domains (domains that do more "research" before accepting email).
Doing a test from testexchangeconnectivity.com doing the outbound smtp test fails on reverse dns saying:
IP Address x.x.x.x does not have a PTR record in DNS
If I do a reverse dns lookup on the IP at iptools.com, it seems to be happy. Also, someone ran a report from dnsstuff.com and I got 3 errors on that report...
1. ERROR: You have one or more MX record(s) that contain an IP address. This is not valid. A fully RFC-compliant mailserver will not be able to send you mail (although some mail servers will, due to the TCP/IP functions that they use). The problem MX records are x.x.x.x
I did change the MX record so it is nowa name, and that name points to the IP of my server. I just pointed the MX to the A record which is my OWA address..
2. ERROR: None of your mail server(s) seem to have reverse DNS (PTR) entries (I didn't get any responses for them). RFC1912 2.1 says you should have a reverse DNS for all your mail servers. It is strongly urged that you have them, as many mailservers will not accept mail from mailservers with no reverse DNS entry. You can double-check using the 'Reverse DNS Lookup' tool (it contacts your servers in real time; the reverse DNS lookups in the DNS report use our local caching DNS server).
3. ERROR: I could not complete a connection to any of your mailservers!
x.x.x.x: Could not connect without glue or A record.<br />
If this is a timeout problem, note that the DNSreport only waits about 40 seconds for responses, so your mail *may* work fine inthis case but you will need to use testing tools specifically designed for such situations to be certain.
pretty sure this was a fluke, emails working fine for 90% of the domains...
Unfortunately ATT hosts my dns for this domain (requirement with their T1 I guess) - so I have limited control of what things I can add/edit, but I can email them to do changes, and they are pretty responsive.