Onexfort emails will only be sent from one email address. If you configure email signatures for your employees, their names and other information will appear in the emails they send. This way, each user's email will be personalised. You have to use the dynamic field {user_email_signature} in your email templates. 

Managing multiple email accounts will be difficult (although this feature is not available), as you will have to forward replies from these email accounts to Onexfort, etc.