As seen in the subject field, It would be a good addition, in my opinion, to be able to create folders for personal mails. If a subject line isn't included within a mail (which is usually the case), then it's very difficult to locate a mail that could be pages and pages through your personal mails. 

Being able to create a folder for certain subjects would make it much easier to sort and find these. I know an archive folder is available, but this could also get incredibly clogged up  if you were a certain age, or very active in sending and receiving mails. 

I have myself experienced the difficulty of looking for one specific No Subject mail in a sea of others, so I agree that there needs to be some way to find a certain mail easier. This would work, along with maybe a search function that you use to find words in the mail itself rather than its subject or the person who sent it.

I've also spent much time searching through emails to find just one. Folders would be a nice touch, and to name them, much like the contact list setup.

One idea you can at least use until a decision is made on this is to forward the message to yourself and include a subject. Only take 5 seconds.