Each employee can access their webmail account by placing /webmail at the end of the website name like:
www.mysite.com/webmail
This will open a username and password box. Then the employee would enter their respective email address (full email address) as the username and then their password. Like so;
User Name:
emp1@mysite.com
Password: XXXXXX
Thats all there is too it.
Cheers-
Andy