change name of stored emails


New Email
I receive several email health letters and often the header name does not reflect the subject of the articles they contain. This makes it extremely hard to find an article about a specefic subject.
I have tried several times to learn how to change the names so I can easily find the content I'm looking for.
I get hits on changing folder names, contact names and everything except what I want.
Can anyone tell me a way to do this? I'm guessing it will require special software and that's OK.