sending text to my cell phone using @tmomail.net no longer working?

We have been experiencing this issue since June.  Some days it works, other days email is rejected.  We have tried getting messages thru using gmail, aol, outlook - all with the same result.  So far T-Mobile has refused to accept responsibility.  They tried to point to gmail…   Not a gmail issue.  Our alarm system has sent these notifications for years with no problem.  Can't get anyone to listen to the issue, since you can't talk with the engineering team, only support help desk.  I have opened a complaint with the BBB and refused to agree to close the ticket until they resolve.  More people should try this route to apply pressure.