Double character spacing

Copying text from an email and pasting it into Writer I get many vertical grey rectangles.
Viewing “Formatting Marks” shows them as extra character spaces

Are these some sort of special spaces? I have tried copying them to Find&Replace but get object not found.

I don’t mind the extra spaces, but I would like to get rid of the grey rectangles in the text.

They’re probably non-breaking spaces. You can get rid of them with a replace with regular expressions. See this article for more information.

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