A few months ago I started getting huge group text spam to hundreds of emails that were almost identical to my own
(changed obviously) if my number was : 123-454-9938 then i would get in a group chat with numbers from 123-454-9900 all the way to 9999. They were using email -> sms specifically which is a relatively new feature that allows you to text mobile devices on carriers that support email to SMS. [1]
Super annoying - but AT&T at a minimum allows you to call and request that they disable this feature for your account. If anyone else is getting constant sms spam from email addresses this is the way.
Disclaimer: I don't know and have not run into any issues where legitimate companies are using this feature yet. If so, then obviously you won't be able to receive those texts. At the moment there is no capability with carriers (that I've seen) that would allow you to create an "allowlist" of domains to accept texts from, but until that exists I won't be dealing with email to sms as it's just a huge cesspit of spam.