There are two places where you can view emails that have been sent to employees.
Via the website
Under Admin, click Email Log, then Email Log again.
This will present you with a listing of all emails that have been sent to employees.
You can view from here if an email has been successfully sent to an employee.
Via the Admin Tool
You can view all emails sent by viewing the Message Log within the Admin Tool.
To do this, follow these steps.
In the Admin Tool, click Message Log.
From here, you have the option to display emails sent between specific dates.
You will also have the ability to resend an email if required.