why does my systemd-services not work?

[Michal Schmidt]

On 06/16/2011 01:07 PM, Reindl Harald wrote:
> you can see the master-porcess and a child shortly in ps aux but
> after a few seconds systemd changes to "deactivating (stop-sigterm)"
> and is killing the processes
...

> [root at testserver:/lib/systemd/system]$ systemctl status dbmail-imapd.service
> dbmail-imapd.service - DBMail IMAP Server
>            Loaded: loaded (/lib/systemd/system/dbmail-imapd.service)
>            Active: deactivating (stop-sigterm) since Thu, 16 Jun 2011 13:05:11 +0200; 1s ago
>           Process: 5013 ExecStart=/usr/sbin/dbmail-imapd (code=exited, status=0/SUCCESS)
>          Main PID: 5014 (code=exited, status=0/SUCCESS)

When the main PID of the service exits, the default action is to kill 
the whole cgroup.
The question is why did the main PID exit in the first place.

Michal