Having issues with using T-Mobile text messaging

When I was with ATT@T I set up a rule in Outlook to alert me via text messaging of important emails but now on T-Mobile its touch and go if it works! I get an error: 550 5.1.1 server temporarily unavailable AUP#MXRT. 

I’m also trying to set up an alert tone when it does work but I’m not sure if I'm setting the tone to the correct contact

Any thoughts ?