NetBSD mail client

[brook%biology.nmsu.edu@localhost (Brook Milligan)]

I have to manage thousands of email messages in my inbox and am
looking for a mail client that will handle this well.  Every one I
have tried so far maintains the messages in mbox format, which leads
to massively large files even when split apart into various folders.
I think it would be better if the messages were managed by the client
in maildir format instead so that each message is a single file.

Are there any recommendations on what would be useful for this?

Thanks alot.

Cheers,
Brook