Thanks for the feedback. I think you are right. Reverse DNS, actually…
I dug a little deeper in the sendmail log and found that my server was identifying itself as ‘local.localdomain’. Some receiving mail servers are fine with this. Others are not. They want to do a look-up on your domain.
The fix (in case anyone else hits this) is to go into your network settings and inspect your host name and domain name. Put in your qualified domain name. Then do a test registration and look in the sendmail log… You should no longer see local.localdomain…
I’ve done these steps and will monitor. But my research suggests this was the root-cause..
