One of my HT servers has stopped delivering email to the others as of this morning, and I am at a total loss to explain why. In the SMTP Send logs, I see that they are negotiating authentication, and then this particular server quits the transaction:
<,250-X-EXPS EXCHANGEAUTH GSSAPI NTLM,
>,X-EXPS EXCHANGEAUTH SHA256 ,
<,235 <authentication information>,
In the queue viewer, it shows the 'last attempt' failure as 451 Primary Target IP address responded with 235 bunch of random characters, which is the auth information from the other server.
It's still delivering to external servers without an issue, but it just won't deliver to the other HT's in the organization. Any ideas?
Thanks in advance