I would like to highlight parts of emails, without having to print them out and use a highlighter pen. I also want to add notes. I ideally want to see the highlights appear when I view an email a second time, so simply forwarding the email to myself and adding let's say a line of stars is not ideal - I'm looking for something more convenient. I know how to do this with PDFs and web pages, but what about emails?
I am willing to consider using whichever software or email client will let me do this on Linux.