xi_service_notification_handler doesn't send notifications

[servicedeskEXV]

Notifications aren't send to configured recipients. Sending a test email works fine. Found a hint in the forum here to tee the output to /tmp.
In this file, the following is logged:
No entry for terminal type "unknown";
using dumb terminal settings.
UNABLE TO EXECUTE QUERY - EXITING!

There seems something wrong with the datase, but what query is it running?
It's the default php handler from Nagios XI that's being used.

[npolovenko]

Hello, @servicedeskEXV. Have notifications ever worked on this server? Can you upload the /var/log/maillog and /usr/local/nagios/var/nagios.log files here? Also, please share the command that you're using to send notifications.

Please go over the following article to make sure that you enabled notifications in "Notification Preferences" and "Notification Methods":
https://assets.nagios.com/downloads/nag ... ios-XI.pdf