The official documentation has been started a long time ago and has evolved aside Modoboa.
According to the important number of questions we received about installation, upgrade and other configuration issues, we realized this documentation was not as clear as we expected. To fix that, a huge rework of the layout and the content has been made and the result …
Modoboa's documentation has been completed with explanations on how to write custom plugins. I hope it is clear enough, do not hesitate to give feedback about it.
Here is a direct link for the lazy ones ;-).