In order for volunteers to 'subscribe' to get their volunteer schedule reminders sent to them in text messages, I have been having them send a text message from their device to an email address - like firstname.lastname@example.org. This way I can both confirm opt-in, and capture their @tomomail.net address to send the texts to later.
This used to work seamlessly, but on my personal tmobile device when I send a text to any email address, I'm now getting a failed message "this service is not available".
You can find all the info you need to get this corrected over here: E-mail to SMS being blocked due to suspected SPAM. We have an Engineer that replies to that thread to get domains whitelisted which is likely why the text to email option isn't working anymore.