In our experience, there are two parts to this out of which one of them is totally under our control. Amber sends out 8 completely different reminder emails based on an employee's interaction with her. These reminders are spread over a span of 2 months giving employees the comfort factor and time to interact with Amber.
The part that's not entirely in our control is how aware are employees of this initiative. We partner with our clients to actively generate awareness using posters and emailers and take care of this part as well.