[Mailman-Developers] Why both a .msg and .db in qfiles?

For every incoming message waiting to be posted, MM writes both a .msg file containing the message text, and a .db file containing meta-information about that message.

I'm curious why MM doesn't just store the rfc822 headers and message body in the .db pickle/marshal as well? Why maintain two files instead of just one?

The reason I ask is because I'm contemplating a similar approach for TMDA.

Thanks.

-- (http://tmda.net/)