Notifications and automatic restarts - No more?

It seems that my custom “Notifications and automatic restarts” email does not get sent properly.

The last I recieved was on feb 17th.

If I command Foris to send a test message the Foris reports Testing message was sent, please check your inbox.
while the system log reports 2017-03-30T16:06:38+02:00 warning []: Missing message-id in rpc-reply.

But no mail is sent.
Using Turris own notification works as before.

Anyone else using a custom notification which do work?
I get the impression that something happened in 3.6.