Exchange 2010 - Invalid RDNS entry.

Malooba
Malooba used Ask the Experts™
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In the last few weeks I have come across a few bounce backs with a #550 Invalid RDNS entry for xxx.xxx.xxx.xxx. The IPv4 address that's given in the bounce back is that of my firewall. When I look at the original message headers though it says the message was received from internalname.domain.local (IPv6 address). When I run a DNS lookup on mail.mydomain.com I get my firewall's public IPv4 address, when I run a rDNS on my firewall's public address & my exchange's public address I get mail.mydomain.com. I am using exchange 2010 and have verified that my send connector's FQDN is set to mail.mydomain.com Any suggestions on what the issue might be?
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AmitIT Architect
Distinguished Expert 2017

Commented:
I assume you didn't created the SPF record? If not created. Follow this
https://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/
Senior Network Consultant / Engineer
Commented:
You need to make sure that the IP you're NATing to has an A record and PTR record setup for it and that they match.

So if you're NATing to 123.45.67.89 then you should have:
- A record mail.mydomain.com point to 123.45.67.89
- PTR 123.45.67.89 point to mail.mydomain.com

The names on the connectors don't really matter here.

Commented:
or

 You have to talk to your ISP to set the reverse DNS record for you.
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Author

Commented:
Yes I have set up my SPF record.

I currently have an A record for my Exchange server's public IP to mail.mydomain.com. Do I need to switch this to my firewall's IP address? I know my current PTR record points to mail.mydomain.com with either of the IP addresses.
Jeremy WeisingerSenior Network Consultant / Engineer

Commented:
I currently have an A record for my Exchange server's public IP to mail.mydomain.com. Do I need to switch this to my firewall's IP address? I know my current PTR record points to mail.mydomain.com with either of the IP addresses.

You can check the SMTP header to verify that the "received from" IP address other servers are seeing match the IP address in your A record and the PTR entry points to the A record.
e.g.
- SMTP header shows "... received from mail.mydomain.com (123.45.67.89) by ..." (this is the IP address your Exchange server is sending from)
- A record is mail.mydomain.com --> 123.45.67.89
- PTR is 123.45.67.89 --> mail.mydomain.com

If any of that does not match up then you will fail the rDNS check.
Seth SimmonsSr. Systems Administrator

Commented:
This question has been classified as abandoned and is closed as part of the Cleanup Program. See the recommendation for more details.

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