I am having trouble with a newly installed server that we have just migrated to. I am running sendmail and cannot send mail to a specific domain. Mail everywhere else appears to work. Logs say:
DSN: Service unavailable
Weirdly, I get a Message accepted for delivery and then a following entry to say DSN: Service Unavailable.
Why would this be? I do not have it relaying through a smart host. The server that I am sending from does not have a public IP and is purely for sending mail from a PHP application.
Any advice appreciated as Google hasn't been a big help.