Thank you for your reaction; alas, the instructions in the link are not the solution but just the beginning of the [problem. I will try to explain myself more clearly:
When I fill in the fields to enable Notifications and click on Test, I see "500 - Internal Server Error"
I copied the error details into Notepad.
Moreover: there is NO /etc/postfix/recipient_canonical on my device.
So this procedure is not the solutions but ends in my problem.
After a fresh install of OMV 6.0.10-1 (Shaitan) on a clean install Armbian on Odroid HC4 (kernel Linux 5.10.81-meson64) I cannot configure System>Notification. When I try to send the test mail I get a 500 - Internal Server Error with details:
Email notification service is disabled.
OMV\Exception: Email notification service is disabled. in /usr/share/openmediavault/engined/rpc/notification.inc:313
Stack trace:
#0 [internal function]: Engined\Rpc\OMVRpcServiceEmailNotification->sendTestEmail(NULL, Array)
#1 /usr/share/php/openmediavault/rpc/serviceabstract.inc(123): call_user_func_array(Array, Array)
#2 /usr/share/php/openmediavault/rpc/rpc.inc(86): OMV\Rpc\ServiceAbstract->callMethod('sendTestEmail', NULL, Array)
#3 /usr/sbin/omv-engined(537): OMV\Rpc\Rpc::call('EmailNotificati...', 'sendTestEmail', NULL, Array, 1)
#4 {main}
Moreover, when checking systemd, I see mdmonitor.service failed with message: mdadm: No mail address or alert command - not monitoring.
To me this also seems related to email configuration.
Any suggestions how to configure the OMV Mail system? 
@hans82 Did you ever made the "writeup" you intended?
I have a clean install of debian 8.6 with kernel 4.1.17-mbl and are ready to have a try at OMV.
