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?