I dont see any error or something else, that would leed me to the root of the problem:
2023-06-12 13:04:29,453 [20] [cmk.base.notify] ----------------------------------------------------------------------
2023-06-12 13:04:29,453 [20] [cmk.base.notify] Got raw notification (host.fqdn.de;Systemd Service Summary) context with 52 variables
2023-06-12 13:04:29,454 [20] [cmk.base.notify] Global rule 'basic notification'...
2023-06-12 13:04:29,454 [20] [cmk.base.notify] -> matches!
2023-06-12 13:04:29,454 [20] [cmk.base.notify] - adding notification of user1, user2, user3, user4, user5, user6, user7, user8, user9 via mail
2023-06-12 13:04:29,454 [20] [cmk.base.notify] Executing 1 notifications:
2023-06-12 13:04:29,454 [20] [cmk.base.notify] * notifying user1, user2, user3, user4, user5, user6, user7, user8, user9 via mail, parameters: from, host_subject, service_subject, elements, no_floating_graphs, graphs_per_notification, notifications_with_graphs, bulk: no
2023-06-12 13:04:29,454 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION: user1,user2,user3,user4,user5,user6,user7,user8,user9;host.fqdn.de;Systemd Service Summary;OK;mail;Total: 148, Disabled: 4, Failed: 0
2023-06-12 13:04:29,455 [20] [cmk.base.notify] executing /omd/sites/sitename/share/check_mk/notifications/mail
2023-06-12 13:04:29,683 [20] [cmk.base.notify] Output: Spooled mail to local mail transmission agent
2023-06-12 13:04:29,707 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION RESULT: user1,user2,user3,user4,user5,user6,user7,user8,user9;host.fqdn.de;Systemd Service Summary;OK;mail;Spooled mail to local mail transmission agent;Spooled mail to local mail transmission agent
2023-06-12 13:04:30,043 [20] [cmk.base.notify] ----------------------------------------------------------------------
2023-06-12 13:04:30,043 [20] [cmk.base.notify] Got raw notification (host.fqdn.de;Systemd Service Summary) context with 52 variables
2023-06-12 13:04:30,044 [20] [cmk.base.notify] Global rule 'basic notification'...
2023-06-12 13:04:30,045 [20] [cmk.base.notify] -> matches!
2023-06-12 13:04:30,045 [20] [cmk.base.notify] - adding notification of user8, user9, user6, user2, user5, user1, user4, user3, user7 via mail
2023-06-12 13:04:30,045 [20] [cmk.base.notify] Executing 1 notifications:
2023-06-12 13:04:30,045 [20] [cmk.base.notify] * notifying user8, user9, user6, user2, user5, user1, user4, user3, user7 via mail, parameters: from, host_subject, service_subject, elements, no_floating_graphs, graphs_per_notification, notifications_with_graphs, bulk: no
2023-06-12 13:04:30,045 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION: user8,user9,user6,user2,user5,user1,user4,user3,user7;host.fqdn.de;Systemd Service Summary;OK;mail;Total: 148, Disabled: 4, Failed: 0
2023-06-12 13:04:30,045 [20] [cmk.base.notify] executing /omd/sites/sitename/share/check_mk/notifications/mail
2023-06-12 13:04:30,252 [20] [cmk.base.notify] Output: Spooled mail to local mail transmission agent
2023-06-12 13:04:30,275 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION RESULT: user8,user9,user6,user2,user5,user1,user4,user3,user7;host.fqdn.de;Systemd Service Summary;OK;mail;Spooled mail to local mail transmission agent;Spooled mail to local mail transmission agent
2023-06-12 13:04:30,580 [20] [cmk.base.notify] ----------------------------------------------------------------------
2023-06-12 13:04:30,580 [20] [cmk.base.notify] Got raw notification (host.fqdn.de;Systemd Service Summary) context with 52 variables
2023-06-12 13:04:30,581 [20] [cmk.base.notify] Global rule 'basic notification'...
2023-06-12 13:04:30,581 [20] [cmk.base.notify] -> matches!
2023-06-12 13:04:30,581 [20] [cmk.base.notify] - adding notification of user9, user7, user6, user1, user3, user8, user4, user5, user2 via mail
2023-06-12 13:04:30,581 [20] [cmk.base.notify] Executing 1 notifications:
2023-06-12 13:04:30,581 [20] [cmk.base.notify] * notifying user9, user7, user6, user1, user3, user8, user4, user5, user2 via mail, parameters: from, host_subject, service_subject, elements, no_floating_graphs, graphs_per_notification, notifications_with_graphs, bulk: no
2023-06-12 13:04:30,581 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION: user9,user7,user6,user1,user3,user8,user4,user5,user2;host.fqdn.de;Systemd Service Summary;OK;mail;Total: 148, Disabled: 4, Failed: 0
2023-06-12 13:04:30,581 [20] [cmk.base.notify] executing /omd/sites/sitename/share/check_mk/notifications/mail
2023-06-12 13:04:30,781 [20] [cmk.base.notify] Output: Spooled mail to local mail transmission agent
2023-06-12 13:04:30,806 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION RESULT: user9,user7,user6,user1,user3,user8,user4,user5,user2;host.fqdn.de;Systemd Service Summary;OK;mail;Spooled mail to local mail transmission agent;Spooled mail to local mail transmission agent
2023-06-12 13:04:31,098 [20] [cmk.base.notify] ----------------------------------------------------------------------
2023-06-12 13:04:31,098 [20] [cmk.base.notify] Got raw notification (host.fqdn.de;Systemd Service Summary) context with 52 variables
2023-06-12 13:04:31,099 [20] [cmk.base.notify] Global rule 'basic notification'...
2023-06-12 13:04:31,099 [20] [cmk.base.notify] -> matches!
2023-06-12 13:04:31,099 [20] [cmk.base.notify] - adding notification of user3, user8, user2, user1, user7, user4, user9, user6, user5 via mail
2023-06-12 13:04:31,099 [20] [cmk.base.notify] Executing 1 notifications:
2023-06-12 13:04:31,100 [20] [cmk.base.notify] * notifying user3, user8, user2, user1, user7, user4, user9, user6, user5 via mail, parameters: from, host_subject, service_subject, elements, no_floating_graphs, graphs_per_notification, notifications_with_graphs, bulk: no
2023-06-12 13:04:31,100 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION: user3,user8,user2,user1,user7,user4,user9,user6,user5;host.fqdn.de;Systemd Service Summary;OK;mail;Total: 148, Disabled: 4, Failed: 0
2023-06-12 13:04:31,100 [20] [cmk.base.notify] executing /omd/sites/sitename/share/check_mk/notifications/mail
2023-06-12 13:04:31,309 [20] [cmk.base.notify] Output: Spooled mail to local mail transmission agent
2023-06-12 13:04:31,332 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION RESULT: user3,user8,user2,user1,user7,user4,user9,user6,user5;host.fqdn.de;Systemd Service Summary;OK;mail;Spooled mail to local mail transmission agent;Spooled mail to local mail transmission agent
2023-06-12 13:04:31,621 [20] [cmk.base.notify] ----------------------------------------------------------------------
2023-06-12 13:04:31,622 [20] [cmk.base.notify] Got raw notification (host.fqdn.de;Systemd Service Summary) context with 52 variables
2023-06-12 13:04:31,623 [20] [cmk.base.notify] Global rule 'basic notification'...
2023-06-12 13:04:31,623 [20] [cmk.base.notify] -> matches!
2023-06-12 13:04:31,623 [20] [cmk.base.notify] - adding notification of user9, user1, user5, user3, user8, user6, user2, user7, user4 via mail
2023-06-12 13:04:31,623 [20] [cmk.base.notify] Executing 1 notifications:
2023-06-12 13:04:31,623 [20] [cmk.base.notify] * notifying user9, user1, user5, user3, user8, user6, user2, user7, user4 via mail, parameters: from, host_subject, service_subject, elements, no_floating_graphs, graphs_per_notification, notifications_with_graphs, bulk: no
2023-06-12 13:04:31,623 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION: user9,user1,user5,user3,user8,user6,user2,user7,user4;host.fqdn.de;Systemd Service Summary;OK;mail;Total: 148, Disabled: 4, Failed: 0
2023-06-12 13:04:31,623 [20] [cmk.base.notify] executing /omd/sites/sitename/share/check_mk/notifications/mail
2023-06-12 13:04:31,832 [20] [cmk.base.notify] Output: Spooled mail to local mail transmission agent
2023-06-12 13:04:31,854 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION RESULT: user9,user1,user5,user3,user8,user6,user2,user7,user4;host.fqdn.de;Systemd Service Summary;OK;mail;Spooled mail to local mail transmission agent;Spooled mail to local mail transmission agent
2023-06-12 13:04:32,147 [20] [cmk.base.notify] ----------------------------------------------------------------------
2023-06-12 13:04:32,147 [20] [cmk.base.notify] Got raw notification (host.fqdn.de;Systemd Service Summary) context with 52 variables
2023-06-12 13:04:32,148 [20] [cmk.base.notify] Global rule 'basic notification'...
2023-06-12 13:04:32,148 [20] [cmk.base.notify] -> matches!
2023-06-12 13:04:32,148 [20] [cmk.base.notify] - adding notification of user5, user2, user4, user7, user9, user8, user6, user3, user1 via mail
2023-06-12 13:04:32,148 [20] [cmk.base.notify] Executing 1 notifications:
2023-06-12 13:04:32,148 [20] [cmk.base.notify] * notifying user5, user2, user4, user7, user9, user8, user6, user3, user1 via mail, parameters: from, host_subject, service_subject, elements, no_floating_graphs, graphs_per_notification, notifications_with_graphs, bulk: no
2023-06-12 13:04:32,149 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION: user5,user2,user4,user7,user9,user8,user6,user3,user1;host.fqdn.de;Systemd Service Summary;OK;mail;Total: 148, Disabled: 4, Failed: 0
2023-06-12 13:04:32,149 [20] [cmk.base.notify] executing /omd/sites/sitename/share/check_mk/notifications/mail
2023-06-12 13:04:32,354 [20] [cmk.base.notify] Output: Spooled mail to local mail transmission agent
2023-06-12 13:04:32,377 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION RESULT: user5,user2,user4,user7,user9,user8,user6,user3,user1;host.fqdn.de;Systemd Service Summary;OK;mail;Spooled mail to local mail transmission agent;Spooled mail to local mail transmission agent
2023-06-12 13:04:32,669 [20] [cmk.base.notify] ----------------------------------------------------------------------
2023-06-12 13:04:32,669 [20] [cmk.base.notify] Got raw notification (host.fqdn.de;Systemd Service Summary) context with 52 variables
2023-06-12 13:04:32,670 [20] [cmk.base.notify] Global rule 'basic notification'...
2023-06-12 13:04:32,670 [20] [cmk.base.notify] -> matches!
2023-06-12 13:04:32,670 [20] [cmk.base.notify] - adding notification of user6, user3, user1, user5, user2, user7, user9, user4, user8 via mail
2023-06-12 13:04:32,670 [20] [cmk.base.notify] Executing 1 notifications:
2023-06-12 13:04:32,670 [20] [cmk.base.notify] * notifying user6, user3, user1, user5, user2, user7, user9, user4, user8 via mail, parameters: from, host_subject, service_subject, elements, no_floating_graphs, graphs_per_notification, notifications_with_graphs, bulk: no
2023-06-12 13:04:32,670 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION: user6,user3,user1,user5,user2,user7,user9,user4,user8;host.fqdn.de;Systemd Service Summary;OK;mail;Total: 148, Disabled: 4, Failed: 0
2023-06-12 13:04:32,671 [20] [cmk.base.notify] executing /omd/sites/sitename/share/check_mk/notifications/mail
2023-06-12 13:04:32,903 [20] [cmk.base.notify] Output: Spooled mail to local mail transmission agent
2023-06-12 13:04:32,924 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION RESULT: user6,user3,user1,user5,user2,user7,user9,user4,user8;host.fqdn.de;Systemd Service Summary;OK;mail;Spooled mail to local mail transmission agent;Spooled mail to local mail transmission agent
2023-06-12 13:04:33,223 [20] [cmk.base.notify] ----------------------------------------------------------------------
2023-06-12 13:04:33,223 [20] [cmk.base.notify] Got raw notification (host.fqdn.de;Systemd Service Summary) context with 52 variables
2023-06-12 13:04:33,224 [20] [cmk.base.notify] Global rule 'basic notification'...
2023-06-12 13:04:33,224 [20] [cmk.base.notify] -> matches!
2023-06-12 13:04:33,224 [20] [cmk.base.notify] - adding notification of user1, user3, user5, user9, user6, user4, user2, user7, user8 via mail
2023-06-12 13:04:33,224 [20] [cmk.base.notify] Executing 1 notifications:
2023-06-12 13:04:33,225 [20] [cmk.base.notify] * notifying user1, user3, user5, user9, user6, user4, user2, user7, user8 via mail, parameters: from, host_subject, service_subject, elements, no_floating_graphs, graphs_per_notification, notifications_with_graphs, bulk: no
2023-06-12 13:04:33,225 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION: user1,user3,user5,user9,user6,user4,user2,user7,user8;host.fqdn.de;Systemd Service Summary;OK;mail;Total: 148, Disabled: 4, Failed: 0
2023-06-12 13:04:33,225 [20] [cmk.base.notify] executing /omd/sites/sitename/share/check_mk/notifications/mail
2023-06-12 13:04:33,441 [20] [cmk.base.notify] Output: Spooled mail to local mail transmission agent
2023-06-12 13:04:33,465 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION RESULT: user1,user3,user5,user9,user6,user4,user2,user7,user8;host.fqdn.de;Systemd Service Summary;OK;mail;Spooled mail to local mail transmission agent;Spooled mail to local mail transmission agent
2023-06-12 13:04:33,760 [20] [cmk.base.notify] ----------------------------------------------------------------------
2023-06-12 13:04:33,760 [20] [cmk.base.notify] Got raw notification (host.fqdn.de;Systemd Service Summary) context with 52 variables
2023-06-12 13:04:33,761 [20] [cmk.base.notify] Global rule 'basic notification'...
2023-06-12 13:04:33,761 [20] [cmk.base.notify] -> matches!
2023-06-12 13:04:33,761 [20] [cmk.base.notify] - adding notification of user4, user5, user3, user6, user7, user1, user9, user8, user2 via mail
2023-06-12 13:04:33,761 [20] [cmk.base.notify] Executing 1 notifications:
2023-06-12 13:04:33,761 [20] [cmk.base.notify] * notifying user4, user5, user3, user6, user7, user1, user9, user8, user2 via mail, parameters: from, host_subject, service_subject, elements, no_floating_graphs, graphs_per_notification, notifications_with_graphs, bulk: no
2023-06-12 13:04:33,762 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION: user4,user5,user3,user6,user7,user1,user9,user8,user2;host.fqdn.de;Systemd Service Summary;OK;mail;Total: 148, Disabled: 4, Failed: 0
2023-06-12 13:04:33,762 [20] [cmk.base.notify] executing /omd/sites/sitename/share/check_mk/notifications/mail
2023-06-12 13:04:33,964 [20] [cmk.base.notify] Output: Spooled mail to local mail transmission agent
2023-06-12 13:04:33,987 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION RESULT: user4,user5,user3,user6,user7,user1,user9,user8,user2;host.fqdn.de;Systemd Service Summary;OK;mail;Spooled mail to local mail transmission agent;Spooled mail to local mail transmission agent
2023-06-12 13:04:34,280 [20] [cmk.base.notify] ----------------------------------------------------------------------
2023-06-12 13:04:34,280 [20] [cmk.base.notify] Got raw notification (host.fqdn.de;Systemd Service Summary) context with 52 variables
2023-06-12 13:04:34,281 [20] [cmk.base.notify] Global rule 'basic notification'...
2023-06-12 13:04:34,281 [20] [cmk.base.notify] -> matches!
2023-06-12 13:04:34,281 [20] [cmk.base.notify] - adding notification of user6, user1, user2, user8, user4, user5, user7, user9, user3 via mail
2023-06-12 13:04:34,282 [20] [cmk.base.notify] Executing 1 notifications:
2023-06-12 13:04:34,282 [20] [cmk.base.notify] * notifying user6, user1, user2, user8, user4, user5, user7, user9, user3 via mail, parameters: from, host_subject, service_subject, elements, no_floating_graphs, graphs_per_notification, notifications_with_graphs, bulk: no
2023-06-12 13:04:34,282 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION: user6,user1,user2,user8,user4,user5,user7,user9,user3;host.fqdn.de;Systemd Service Summary;OK;mail;Total: 148, Disabled: 4, Failed: 0
2023-06-12 13:04:34,282 [20] [cmk.base.notify] executing /omd/sites/sitename/share/check_mk/notifications/mail
2023-06-12 13:04:34,550 [20] [cmk.base.notify] Output: Spooled mail to local mail transmission agent
2023-06-12 13:04:34,572 [20] [cmk.utils.notify] sending command LOG;SERVICE NOTIFICATION RESULT: user6,user1,user2,user8,user4,user5,user7,user9,user3;host.fqdn.de;Systemd Service Summary;OK;mail;Spooled mail to local mail transmission agent;Spooled mail to local mail transmission agent
Settings in Notification configuration → basic notification
Rule properties:Description: basic notification
Notification method:Notification Method: HTML
Notification method:Notification Method:Create Notification with the following parameters:From:Email address: example@fqdn.de
Notification method:Notification Method:Create Notification with the following parameters:From:Display Name: Senders Name
Notification method:Notification Method:Create Notification with the following parameters:Subject for service notification: Check_MK: $HOSTNAME$ - $EVENT_TXT$
Notification method:Notification Method:Create Notification with the following parameters:Subject for service notifications: Check_MK: $HOSTNAME$/$SERVICEDESC$ $EVENT_TXT$
Notification method:Notification Method:Create Notification with the following parameters:Display additional information:
- IP Address of Host
- Absolute Time of Alert
- Additional Plugin Output
- Acknowledgement Author
- Acknowledgement Comment
- Notification Author
- Notification Comment
- Time series graph
Notification method:Notification Method:Create Notification with the following parameters:Display graphs among each other
Contact selection: Notify all contacts of the notified host or service.