Posted 9/14/2018 17:13 (#6988125 - in reply to #6988026) Subject: MXToolBox - a useful site, but not for the faint of heart
The big challenge is to find out why the e-mail isn't hitting PA.net. E-mails that don't make it through are floating somewhere between here and Russia or North Korea.
I like the potential "Header Analyzer" for your needs. You may find some hints by copying/pasting the headers of your test e-mails in and compare the results.
The key point is the e-mails you are not getting are not "bouncing back" to the sender. That fact smells like a blacklist issue, as e-mails hitting blacklisted domains will not be bounced back. If the issue is a spammer, the bounce-back traffic would cripple the e-mail systems.