Found in var/log/notify.log a relevant message:
2020-06-29 08:01:07 Notification plugin did not finish within 60 seconds. Terminating.
2020-06-29 08:01:07 ERROR: script /omd/sites/mastersite/share/check_mk/notifications/mail --bulk returned with exit code 1
Nothing in /var/log/maillog to this item.
Any ideas?
Kind regards
Hermann M.