There are several public mailinglists available to get in touch with the OMD developers and other OMD users:
The OMD users mailinglist is meant to be the official place for OMD users to exchange with eachother.
The OMD developer mailinglist is the official list to get in touch with the OMD developers. You may report bugs, discuss new features and so on there.
The omd commit list is a pure read-only mailinglist. All commits to the master branch of the OMD git are sent to this list.
OMD has a dedicated board on monitoring-Portal.org: OMD - Open Monitoring Distribution
The Monitoring Portal is mainly in German language but you are welcome to post in English.