we are urgently searching for a community developer to maintain especially the IMAP, CalDAV and CardDAV backends.
Unfortunately the developer who took care of these earlier stopped contributing to Z-Push (due to personal reasons).
These backends get a lot of new users with (mostly minor) issues. We don't have enough resources to take care of them.
If you are interested, please join our Community Developer Meeting. More information is here:
There is a "how to start" wiki page: https://wiki.z-hub.io/display/ZP/Development+guidelines
Some issues we have tickets for: