we have two exchange 2013 servers in dag group. one server has a receive connector that we point all of our devices that email to, such as copiers, and our AS400 server, so they relay through that connector, then out through exchange.
I have a couple of domains we email to suddenly not accepting our emails. sbcglobal being one.
first error I see is: 451 4.1.8 Possibly forged hostname for 209.156.40.158
second error I see is :450 4.7.1 Client host rejected: cannot find your hostname, [209.156.40.158]
but that is the IP address of our WAN connection to the internet, not our MX record.
now, if I go to mxtoolbox and run through all of their checks, reverse dns works.
the only errors I have are for DMARC, missing or invalid record, SPF is not setup, DNS, SOA expire value out of recommended range, and SMTP, does not support TLS.
and we have not changed anything in our setup since we added the second exchange server many months ago, so not sure why suddenly we have these errors.
can someone point me in right direction?