[Dovecot] Proprietary mail storage.

I have a large existing read-only collection of mails packaged in individual zip files as <rfc822 file>+<some additional info>. Is it possible (and how difficult) to create a proprietary plugin (like gzip) which will open a zip file, extract mail and pass it back to Dovecot? Where do I start? If plugin is not the right approach, what is? Another question is how will this affect Dovecot performance and how to avoid any significant degradation. Any help is appreciated.Thanks.