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Cannot resolve PTR record for x.x.x.x

I'm getting the following error when sending to only a couple of recipients

"You do not have permission to send to this recipient.  For assistance, contact your system administrator.
            <xyz.123.com#5.7.1 smtp;550 5.7.1 Access denied. Cannot resolve PTR record for x.x.x.x>"

The server name and IPs have been changed for security reasons.

can someone guide me on where to start in troublshooting this issue. We are waiting for a real email admin to start soon and I'm just covering till then. Thank you.
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2 Solutions
Alan HardistyCo-OwnerCommented:
centemAuthor Commented:
I read your article and it was helpful. It appears that our mail server is setup correctly. There are only two email addresses that our users reported to have this issue. We can send email just fine to everyone else.

Are there some dns checking I can do from our email server to test that resolution to their mail server is correct?
Alan HardistyCo-OwnerCommented:
Good - that's encouraging.

You can use nslookup on your server from a command prompt:

nslookup mail.theirdomain.com.

To find out their mail server names, you can use www.mxtoolbox.com to find out their MX records / mail server names.
Renato Montenegro RusticiIT SpecialistCommented:

It looks like you dont have a valid reverse IP address. Some mail exchangers do require that configuration.

Make sure your outgoing IP address (the one used to send messages out to the Internet) has a name and that name matches the IP address.


sender.mydomain.com must have an ip address pointing to
and must point to sender.mydomain.com

You can check this out using nslookup or other online tools, like this one:

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