Conditions:
Maintenance Status = Not in Maintenance
Trigger Value = Problem
Trigger Severity >= Informational

Operations:
Default Step Duration: 60 Secs
Steps 1 to 1
Step Duration: 60 seconds
Operation Type: Send Message
Send to Groups: Zabbix Administrators
Send only to: Email
Default message is CHECKED.
Conditions: Event Acknowledged = ack

When an event occurs I log in to the portal, and then acknowledge teh event. The email does not get generated and sent out.

If I change the parameters to NOT ACKNOWLEDGED, the email is generated and sent as I would expect, so I know everything is configured properly.