A long time ago when I was using an other OS I also used Altavista Personal to index my email. Worked great. I've found a couple of tools (htdig, glimpse) for linux that index files. I haven't researched theese tools that deeply because it seams like they both index entire files rather than separate email messages within a large mbox file.
Ideas, anyone? -- oivvio polite cell +46 (0)709 30 40 30 / phone +46 (0)8 669 64 18 / fax +46 (0)8 84 00 18 varvsgatan 10A / s-117 29 stockholm / sweden