[Dovecot] New Mailbox Format Plugin Help

[Sacha Bernstein]

I would like to develop a new mailbox format for a very specialized
application.  Can anyone point me in the appropriate direction to get
started writing a plugin?

More detail for anyone interested:
I need to store mail in a format that's quickly accessible and
modifiable to an external process.  This is for a very low-volume mail
system (averaging less than 50 messages stored at any one time) that
needs very good indexing.  I need to create new mailboxes on the fly
and perform fast searches across all the mailboxes.  I intend to store
all the messages in an SQL database.  Any help getting started
interfacing with dovecot (other than reading through _all_ the source
code) would be greatly appreciated.

Thanks,
Sacha