Email to MULTIPLE ADDRESSES not delivered

Perhaps the forum can help me.  I have not had much luck on the phone.

 

We maintain a mailing list for a small organization.  Once in a while (once a week to once a month), we send out a notice to the group for some reason.

 

The group is about 125 addresses.  We know that we can only send 100 at a time, so we maintain two lists, one with about 95 addresses, and the second with the rest.  We bcc the addresses to protect our subscribers' privacy.

 

We've been doing this successfully for three years.  Most recently on 20 Sep 2019.

 

On September 26, our e-mails stopped going through. 

 

Although we usually use Outlook to send the e-mails, we have also tried from Xfinity Mail web interface, and got the same result.

 

I can send the same e-mail to a SINGLE address (as a bcc), and it goes through fine.  This proves it is NOT the mail client, or anything magic in the content of the e-mail, or the size of the e-mail (in this case, approximately 24K . . . three orders of magnitude less than the Xfinity limit).

 

We did have a single bad address in one of our lists.  So whenever we sent out an e-mail to the list, we would get back an error for that one address.  When we include the bad address now, we STILL get back an error for that address (proving that it is getting to the server), but none of the other e-mails get delivered.  Removing the bad address stopped the error, but still none of the messages were delivered.

 

I have talked to customer service several times.  I have, I believe, three open tickets currently, some of which have been "escalated", if that means anything. 

 

I'm stumped, and I think customer service is, too.  The only think I can think of is that the Xfinity spam detector has flagged us (incorrectly . . . REALLY) as spammers, and is refusing to deliver anything.  Customer service says that's not possible.

 

Anybody got any bright ideas?