Email SQL Job Notification to Multiple Recipients

It's actually quite simply if you tried it

1. Create a New Operator
SQL Server Agent -> Operators -> right-click -> New Operator

2. Choose a Name (e.g. "Group") and enter multiple emails in the E-mail name: field, separated by ;
a@gmail.com; b@gmail.com

3. In your SQL Job Notification, select "Group" as Operator and that's it

Source
http://www.dbanation.com/?p=416