Despite all the buzz about Gmail, there are other email search engines. Two years ago at the London MacExpo, I went to a presentation by Creo on their email search engine, Six Degrees. At that time, Six Degrees was a stand-alone application, which could only import email from Microsoft's Entourage. I didn't use Entourage, but even so, I was excited by the possibilities of the software. Now Creo have launched Six Degrees 2.0, and there are some major changes. It runs as a local server (Jakarta Tomcat, to be precise) which you connect to using your web browser, and sift through the database using an HTML front-end. Better still, you can now import mail from a variety of different email clients, and also Unix
mbox files, which should make importing possible from any application. It can also check POP and IMAP servers directly and sync with IMAP folders, so that once you have imported your old email, it will update its database automatically as new messages are delivered and sent.
You can search by message, attached file or person in addition to a general search that includes everything. As the text of emails is indexed as well, you can be pretty sure of finding anything you need. Once you click on a message, person or file, you get a page with the contextual relationships around that item. So there's a list of all the emails in that thread, other participants in the conversation, attachments, links in the emails and so on. This is really the killer feature. Mailsmith — my preferred email client — has great and rather powerful searching capabilities, but it tends to be best at finding fairly specific things. If you know what you're looking for, that's great, but disturbingly often I only have the vaguest concept of what I'm searching for. In the full (paid for) version, there's also the 'To Do' and 'Projects' features, which allow you to flag important messages to find them quickly (in the case of the former), and create dynamic collections of emails, people and files in the case of the latter. If you tag an email with a certain subject to be included in one project, any email with that subject gets automatically added. This allows you to do something I've always wanted, which is to file something in more than one 'box' at the same time. Other nice features include being able to save complex custom searches to re-use later, and to be able to view all messages from a particular domain, which is great when you want to isolate all correspondence with a particular company.
There are a few rough edges, as might be expected with such a comprehensive re-write of a product. The documentation is very thin, and I haven't found a way to search within a results set yet, which would be handy when you realise you needed another term to restrict the search a bit more. However, all in all it's an impressive and useful piece of software. The 'light' version is free, and for many people would be perfectly adequate for their needs.
If you'd rather go with Open Source, there's Zoé, which does very similar things. There's a good review here, to which I would add that — at least on my machine — the latest version of Zoé eats up far too many CPU cycles (around 50%). Again, it's rather sparsely documented, so you have to rely on your native intelligence when exploring the interface.