Depending on how many different SMS recipients you are sending to, you can send them via the carrier provided service.
For example, I send SMS to myself and my wife often via outlook email using their carrier provided email to SMS address. This is simple since I know our carriers.
You can google "email to sms verizon tmobile etc..." to get carrier specific connector addresses. Example: 1234567890@vztext.com
Here is a list of some carriers and their SMS/MMS gateway domains: https://www.digitaltrends.com/mobile/how-to-send-e-mail-to-sms-text/
If I were sending to many people, this may not be a good solution. I have used this well for server alerting to a small group of team members via sms, or sending a reminders to myself or wife.
1One thing: replying to messages sent like this needs MMS. SMS cannot send to an email address – derz00 – 2017-10-30T18:42:28.327
I know I can do that, but I am looking for something that would keep the conversation thread. – TomEus – 2017-11-02T21:21:11.277
Because an SMS technically is restricted to 160 characters, you'll want MMS unless the conversation thread is VERY short. Please excuse my sarcasm. I'm not sure what it means to "keep the conversation thread" and can not probably help any further. – CoreyJJohnson – 2018-01-30T18:46:48.620