If you want to give the visitors option to unsubscribe then download this contribution "Newsletter unsubscribe", install it and after that follow the instructions in readme - file attached.

There are perhaps better ways of doing what I have done, as I am quite noob to php. But it is working for me.

This is only the readme - file, not the whole package.
I have installed "Simple Visitor Newsletter with HTML Support" version 2.0

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