ReMail does this.
It's actually not hard and was in an internal version of Gmail for years. I guess the problem with it is then people learn to ignore any message not highlighted, so that when you get that one urgent email from a new sender you're prone to miss it.
ReMail does this.
It's actually not hard and was in an internal version of Gmail for years. I guess the problem with it is then people learn to ignore any message not highlighted, so that when you get that one urgent email from a new sender you're prone to miss it.