Who I have the same questioned this topic

Hello... I operate a service that sends text notifications for local volunteer and career firefighters when we get a call. It has been working perfectly up until this weekend, when the text notifications for Verizon started to fail... I use the cell-number @VTEXT.com address. I've already verified that our domain is not blacklisted as spam, and that all the proper domain entries are there as needed. We only send notifications when a call is generated (about 10 per day, and somewhere around 80 users for 6 different departments)… so not a huge message pool.

We are getting failure messages like:

554 vzw-ibgw-5003a.stratus.cloudmark.com cmsmtp ESMTP server not available - POL102 - 4CgljYVY4jhDy

It is ONLY Verizon messages that are failing... Any idea why this is occurring and what I can to do restore this service? This isn't necessarily critical for life safety, but its a very important service for our local firefighters.