Every time you receive a new text message it will be automatically appended to a text file.
Then
Append text to file
This action will append to a text file as determined by the filename and folder path you specify. If there is no file present, a new file will be created. Once a file’s size reaches to maximum a new file will be created.
ID XtC39LTE
Explore more great ways to automate QNAP and Android SMS