YouMail allows you to set special greetings for any and all blocked and unknown callers without you needing to set greetings for each individually. Just follow these steps to set up this feature on the YouMail website.
1. Log into your YouMail acount and click on "Greetings" on the left hand side.
2. Select "Private Numbers" and click the "Edit" button to set up how you want callers with a private number or blocked caller ID to be greeted. Save when you're done.