Issuing named-user licenses problem - email invites not getting delivered anymore

I'm trying to assign named-user licenses via the console at https://creative.adobe.com.  It worked for a few accounts for our org fine, now for the last week or so the emails are not coming through.

When it was working emails were coming to us with the following type of info in the headers...

Received: from a14-30.smtp-out.amazonses.com (a14-30.smtp-out.amazonses.com [54.240.14.30])

From: Adobe Systems Incorporated  <message@adobe.com>

Reply-To: Adobe Systems Incorporated <message@adobe.com>

Message-ID: <00000152696a6b59-aafb2954-bb9f-442c-aa6c-a15d5065b92a-000000@email.amazonses.com>

Subject: Welcome to Acrobat Standard DC

I've whitelisted amazonses.com and adobe.com in our spam firewall but I still do not see email in the logs with this type of profile even after multiple 'Click to resend' attempts.

I've gone through the info here...

Didn't receive expected e-mail from Adobe

...to no avail.  I also believe this info is out of date as no mention is made of the amazonses.com IP addresses it looks like they are using for this process now.

I have opened a case with Adobe but they are pretty adamant 'the problem is on your end'.  They will not produce any logs or errors showing what type of problem they are having connecting to our mail server or sending email to us.