Emails vertical line

[Coldicote]

Down the left side of emails there is often a vertical black line, or a line of pointers or dots. Mine shows dots but I would like to change it to a simple line. I know it's there somewhere but can't find it. How do I change it please?

[boxtops]

I get a vertical line when someone has forwarded something to me - I don't know what you can do about it.

[Coldicote]

At one time messages on my PC showed the black line, but something I did changed it. I remember there being an option between the simple black line, or a verticle line of >> (which took up too much room) or a vertical line of :: Wish I hadn't done it and would like to get it back to the simple line, but cannot find how.