How do you organize your email? Always afraid to delete something I will need later

My inbox normally contains about half a dozen messages that require that I do something in order to respond to them. I treat it as a to-do list, pretty much.

Messages that I want to save go into my saved-messages mailbox. Every year, I start a new one and re-name the old one to saved-messages-YYYY (where YYYY is the year).

Anything that I expect to need for future reference gets saved as a text file and stored in a filesystem. I try not to treat my saved-messages mailboxes as an information database, but I do occasionally need to search through them.

I delete obvious spam and useless messages.

I know that some people spend an inordinate amount of time organizing email into mailboxes, but I just don't think that it is a very good way to store information.