The Email Address on the voicemail server doesn't appear to matter, in fact it can be blank.
Try this, it works for Audix, haven't tested on IA770/CMM but I will, don't have S8400 though, only 8300.
Check the Permissions on the vmb specifically IMAPI Message Transfer (unsure if this affects)
Control Panel / Mail
E-Mail Accounts / New / MS Exchange, POP3,IMAP,HTTP / next
Select "Manually Configure Server settings"
Your Name : Joe Bloggs
E-Mail Address : Joe_Blogs@companymail.com (standard email address)
Account Type : POP3
Incoming Mail Server : 10.x.x.x (your Audix/CMM server)
Outgoing Mail Server : same as above
Username : (the extension/voicemail number)
Password : (the voicemail extension pwd)
Remember Password : ticked
"Test Account Settings" - Log into incoming mail server success? cancel the other tests.
*note if vmb passsword changes, change it here as well.
More Settings
/General - Name : "Voicemail"
/Outgoing Server : Use Same settings
/Connection : Connect using LAN
/Advanced : Incoming Server (POP3) = 110
Outgoing Server = 25
Leave copy on server = up to you.
Once created go back to E-Mail Accounts/E-Mail, select the account and change the folder location to where you want the mail delivered.
*Note, vm's are delivered as an attachment with .lvp extension, there wasn't an app to play this on a blackberry last time I looked (a while ago now)