I am not sure what do you really want and i dont know which email requirements has vtiger. But if you only need SMTP and IMAP service the previous link is overkill, to get them you dont need either to instal lfetchmail or modify any stub file.
You only have to:
a) enable users and mail modules
b) in mail create a virtual mail domain, enable authorization and enable imap service
c) create users amnd edit them to add a mail address in the virtual domain.
This will be a basic email configuration with eBox but as I said I am not sure what are your requirements...