Hi Martin,
On the current eBox version, if you don't enable a module, you are telling eBox not to manage the service. That's why amavis is running even though the modules are disabled.
In the past the working mode wasn't the same. It worked as follows:if the module was disabled the associated services wouldn't be running.
This change was caused for a few modifications we had to make to comply with the ubuntu policy.
We are already working on approach that will allow you to stop the service if you are not using it while still complying with the above requirements.
As a temporary workaround you can manually stop the services you are not using. For example to stop amavis:
/etc/init.d/amavis stop
Don't hesitate to ask us if you need further help