Messenger - How to not automatically turn group messages into MMS? How do I prevent the lollipop (5.1) from turning my group messages into MMS?
I have some friends who can't receive MMS so this is a bit peeving. 

This question has been asked before but not answered, or is for previous versions and no longer applicable.
This is applicable to Google Messenger version 1.8.268 updated on 17 May 2016.

Go to Settings>Advanced>MMS>Group messaging

Select "Send individual SMS messages..."

Hope this helps.