[AC Question]

I am trying to use an alternative to the embedded Messenger app. I have tried SMS Composer and Old School SMS. No matter which app I use I can't delete or set to 'read' any of the SMS's I receive.
I want to avoid Messnger since I prefer unthreaded messaging and Messenger does not support unthreaded views.
Could someone suggest a method or app that would allow me to fully manage my SMS's without having to leave Messenger running in the background for use in deleting and otherwise managing the state of the actual SMS messages.

I have tried disabling the Messenger app but this prevents SMS's from appearing in any of the apps I have installed.

I am running a Sony Xperia Z3 Compact Android v4.4.4 . Messenger app v 28.0.C.1.10 .

[Rukbat]

I have tried disabling the Messenger app but this prevents SMS's from appearing in any of the apps I have installed.

Most SMS apps call processes in the default app to do the actual SMS communication, they're just UIs for that function. As far as deleting an SMS, you should be able to do that by long-pressing the message and choosing delete. It sometimes still shows, but if you close Messenger, then reopen it, it shows the message deleted. (But it does delete the entire conversation, not individual texts.)