Ask HN: SQL based e-mail clients?

I have almost 20 years worth of e-mail. I probably don't need it all.

However, e-mail clients change. Sometimes I change my primary OS. Currently I am on OS X.

I am looking for an e-mail client that uses SQLite or SQL based backend. Everything I have is in .mbox, so pretty portable. But, if I could fire up a SQL tool and run queries, I could always have access to my e-mail, client agnostic.

Does anyone know of anything that exists?