Exchange 2010, SMTP Reverse DNS Mismatch

Posted on 2014-03-25
Medium Priority
Last Modified: 2014-11-12
Hi Expert,

There is a domain that queue inside my server, unable to send out, there is an error while i check their inbound traffic through exchange test connectivity, but when i use yahoo,gmail send, is working.

After that, i use mxtoolbox to check my mx record, i get this,

SMTP Reverse DNS Mismatch      Warning - Reverse DNS does not match SMTP Banner

could it cause the email not able to send out because of this warning ? and how can i fix this warning.

Question by:patcheah
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Expert Comment

ID: 39953454
Yes, some ISP's mark this "mismatch" as spam.

To Configure the smtp banner for the domain you are trying to send from:

Configure SMTP banner Exchange 2007/2010

 1. Open the Exchange management console.
 2. Select the Organisation Configuration container.
 3. Select Hub Transport container.
 4. On the right select the Send Connectors tab.
 5. Right click your send connector and select properties.
 6. On the General tab under the Set the Fully Qualified Domain Name (FQDN) this connector will… type the A record domain name you created. Which in our case is mail.yourdomain.com. Click OK.
 7. Under the Server Configuration container click the Hub Transport container.
 8. In the Right window Select the properties of the Receive Connector under Receive Connectors tab.
 9. On the General tab under the Set the Fully Qualified Domain Name (FQDN) this connector will… type the A record domain name you created. Which in our case is mail.yourdomain.com. Click OK.
LVL 14

Expert Comment

by:Andy M
ID: 39953561
A reverse dns is handled by your Internet Provider. Basically your email server will use an internet line which will have an IP address (i.e. This IP address will resolve to a hostname (i.e. google-public-dns-a.google.com). This can be checked by using NSLOOKUP.

What the error is refering to is that the reverse dns hostname does not match the FQDN of your email server (the SMTP banner). Your banner may be set to mail.domain.com but the reverse dns may be set to randomnumber-isp.com or something like this. Many email servers are configured to suspect this to be possible spam.

You need to contact your ISP and get them to change the hostname of your IP address to match the SMTP banner/fqdn of your mail server. Note some ISP's do not have this facility, in which case you may need to use a smarthost service or change ISP's.
LVL 40

Expert Comment

ID: 39953794
Services like MXToolbox are testing your receive connector for this test.  Ignore this result!

If you want to test what your send connector is set to, follow the instructions at http://cbl.abuseat.org/helocheck.html to send an email and you will get a response showing the info.

At that point you can test for a match between the SMTP banner on the send connector and your PTR record by typing something like the following (using an example where your SMTP banner is set to "mail.domain.com") :
nslookup mail.domain.com
The IP from this should match the IP reported in the HELO check email.

And then using the IP that is reported in the HELO check email (substitute for x.x.x.x below):
nslookup -q=ptr x.x.x.x
This should give a FQDN that matches the SMTP banner.
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LVL 12

Expert Comment

by:Md. Mojahid
ID: 39955487
Ask to service provider to create record for smtp banner with your external domain.
like owa.yourdmain.com

Author Comment

ID: 39957973
Hi Expert,

Thanks for the value advise, in my case, we are renting our server in data center, we manage our own exchange, can the data center help  to change the hostname of  IP address to match the SMTP banner/fqdn of my mail server?

LVL 40

Accepted Solution

footech earned 1500 total points
ID: 39958488
I would say in the majority of cases, whoever has leased the public IP address to you will be the one to contact in order to change the PTR record.
Only you can answer where your other DNS records are managed.  It could be where you from wherever you purchased/registered your domain name.  Sometimes this can be a company that hosts your website.  It's also possible to split off your DNS management to a completely separate company, but if you had done this you probably wouldn't be asking.

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