Memiks a new user of opensmtpd and question about rspamd

[Mémîks]

Hello,

I am a new user of opensmtpd and I really like it.

I would like to create a filter to interact with rspamd or a plugin...
Do you know where I can find some documentation about development of opensmtpd?

Thanks a lot,
BR,
Frédéric LESUR.