Who I have the same questioned this topic

I have an application that sends short messages via e-mail to text to my team.  On June 21, between 9:42 am and 10:04pm this service stopped working, but only for my team's phone numbers, (all verizon) and only from my two specific mail servers.  There are other people on campus using my mail servers for similar messages via vtext, and they continue to be delivered.  If I send email via outlook365 to my team's numbers, it also works fine.  The mail log message changed from 'mail accepted for delivery' to 'service unavailable'.  Sending to vzwpix.com has the same error.  It seems that vtext is blocking messages to my number, but only if it is from a certain mail server.