This is a old thread and you should probably start your own thread with your own environment details and setup information. (Such as: Version of osTicket, version of PHP, webserver, autoresponder settings, alerts and notices settings, and email setup).
There is no such thing as an "Admin user" in osTicket. There are two types of accounts which are: Users and Agents. Agents can have the Admin flag. Being an Admin does not have anything to do with if they get Agent ticket alerts.