A client of mine recently moved from on-premise Exchange to Office 365 for email.
They occasionally send emails to the text addresses of a small group of their own employees.
Since the move, they have had intermittent issues with SMS messages being rejected as spam by T-Mobile.
I see that a recent thread on this subject was closed E-mail to SMS being blocked due to suspected SPAM
srickar You were helping people with similar issues and I've sent you a connection request hoping you can help with mine also.