Voicemail To Email Question

I recently implemented vmail to email but for one reason or the other when i receive the audio file as email it appears to be coming from asterisk@example.com as pasted below

Return-Path: asterisk@example.com
Authentication-Results: mta251.mail.re2.yahoo.com from=asterisk.example.com; domainkeys=neutral (no sig)
Received: from (EHLO yb-server.example.com)

My question is where do i make changes so that the true email of my domain is reflected there so that the email does not appear to be spam



its the serveremail= setting in voicemail.conf