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Malooba
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Exchange 2010 - Invalid RDNS entry.

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?
ExchangeDNSWindows Server 2008

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Seth Simmons

8/22/2022 - Mon
Amit

I assume you didn't created the SPF record? If not created. Follow this
https://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/
ASKER CERTIFIED SOLUTION
Jeremy Weisinger

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Deorali

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

ASKER
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.
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Jeremy Weisinger

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 Simmons

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