Alerter doesn't output any logs to zabbix_server.log at this moment, so there is no way to know if alerter has:

• a lot of backlog of alerts
• smtp server reject connection or any other mediatype error

I think it's good that alerter output following logs to zabbix_server.log

• number of alerts that alerter try to execute
• mediatype error (smtp connection error, cannot execute script, etc)