Browse to http://mymessages.wireless.att.com
Sign in using your Mobile Number and Password. If you do not already have online access to your account, click Register now.
Make sure that ”Block all text messages sent to you as email” DOES NOT have a check in the box.
Add the domain “textcaster.com” to the Allow List box.
Hit the Submit button at the bottom of the page.
Contact TextCaster Customer Support for follow up testing.