When you log into the server admin
https://hostname/admin and modify the extension (Extensions > Modify Extensions > Modify (ext)), those features that are enabled are for what the user is allowed to do. You can grant or deny those permissions for that user on that extension. Make sure the email address is specified here. While still on the server admin, under System Setup > Voicemail settings, you'll need to fill in a "From" address (this can be a bunk email address in most cases, I use
switchvox@domainname.com), the SMTP server will need to be also filled in. This needs to be correct and valid. Username and password I dont think needs to be correct, as mine is not. I may have just used the Switchvox Server admin username and password, I dont remember. I may have even left it default
If you log into the web admin for the actual extension
https://hostname/main, log in with the extension credentials, you will also need to set up the email address under Settings > Modify Account
I hope this helps