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Reverse DNS failed on mxtoolbox

Posted on 2009-03-30
Medium Priority
Last Modified: 2012-05-06
We just got a new IP from the ISP since we switched to a T1 line and I ran a test using mxtoolbox.com on our mail server and I got a rev dns failed. What is this? IP to domain name? How can i fix this or does it need to be fixed?

RESULT: mail.woodlandsprep.org
Banner: 220 barracuda.woodlandsprep.org ESMTP (69e64d74d20ea39f808266de067fe9e8)
Connect Time: 0 seconds - Good
Transaction Time: 0.094 seconds - Good
Relay Check: OK - This server is not an open relay.
Rev DNS Check: Reverse DNS FAILED! This is a problem.
GeoCode Info: Geocoding server is unavailable
Session Transcript: HELO please-read-policy.mxtoolbox.com
250 barracuda.woodlandsprep.org Hello mxtb-pws1.mxtoolbox.com [], pleased to meet y [16 ms]
MAIL FROM: <test@mxtoolbox.com>
250 [16 ms]
RCPT TO: <test@mxtoolbox.com>
550 No such domain at this location (test@mxtoolbox.co [62 ms]
221 B [0 ms]
Question by:ravenrx7
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Accepted Solution

csaint00 earned 1500 total points
ID: 24018677
Not sure if this error refers to your internal DNS or the ISPs, you can contact your ISP and have them put a Reverse DNS entry into their reverse lookup zone which will probably fix this error. Though generally reverse DNS isn't required by much.

Author Comment

ID: 24018748
if we changed ip addesses do you  think this would effect sending emails to comcast and aol users. I've already went into domain name registrar and changed the ip on our mx record

Expert Comment

ID: 24018830
Reverse IP allows you to lookup the domain name or address associated with that IP.

A fictional example is:- If you lookup the IP address for www.google.com and the IP address is, then you enter into a reverse IP lookup, you should get www.google.com.

You can usually change your IP address by contacting your ISP.

Since Spammers usually send Spam without the permission of their ISP, they dont usually bother changing their Reverse IP address entry.

The reason MXToolbox displayed a warning is that if your reverse IP doesnt match your domain name, some companies think that it is an indication of spam being sent and block your emails.

Hope that helps.
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Author Comment

ID: 24018841
I found this on AOL's site
Error 421 DNS:NR

421 DNS:NR

Reverse DNS lookup for your IP address is failing. AOL does require that all connecting Mail Transfer Agents have established reverse DNS.


Reverse DNS is a way of associating an IP address with its domain name. The reverse DNS identifier is contained in the PTR portion of the IP Zone File. You may look at your reverse DNS using our reverse DNS search tool.

If you are on a dynamic IP address, please call your ISP and request a static IP address with proper rDNS before attempting to send mail to AOL through that server.

If you are on a static IP address, please call your ISP or DNS provider and ask them to establish a reverse DNS record for your IP address, reflecting your correct domain name.

For additional information on reverse DNS, please visit http://postmaster.info.aol.com/info/rdns.html .


Expert Comment

ID: 24018845
The warning is not related to your MX records.

Expert Comment

ID: 24018884
You can resolve that aol error by contacting your ISP and ask them to add your domain to the reverse IP address table.

Expert Comment

ID: 24018975
... you're stealing my thunder Dan

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