If you want to search things -- dates, senders, URLs, related text, whatever -- quickly, you need to build an index. Looking through 2GB of e-mail on the fly to see what other stuff this person sent will take way too long. You could create your own indexing system, but there's not much point when free databases are available.

It's pretty easy to make your mail system run a script to index each new e-mail you get when it arrives, or to look through your mailbox once an hour and add anything that's new.