One of my customers is complaining that some of their clients are not receiving auto-responders.   When I look through the delivery logs, it shows the auto-responders sending to some domains and not others.   While they are limited to sending 1 auto-response per email address per day, it isn't even sending the first one out.

 

As a test, I set up an email address on a different domain and enabled auto-responders on the test email and my customers email.  I then had the client send us a test message.   We both received the message, but the delivery logs did not show any autoresponde.   When I sent a test from a gmail account, it worked fine.

 

Is there a reason why SM would send to some domains and not others?