We had to figure out why a customers emails stopped. They have three domains aliased. They wouldn’t get emails with Domain name #1, but they would get them from Domain names #2 and #3.
We went to the website “http://mxtoolbox.com“, put in their domain name and found that domain name got black listed. One of the issues that will trigger this is Unsolicited Bulk Email (UBE). This can cause entire ranges can be reported as blacklisted.
Haven’t figured out at resolution the problem, but wanted to share the information about this service.
Another site that I found helpful with figuring out email issues is http://mailtester.com/.
I hope this helps someone else out there…