Your staff may visit your unique web portal to log in and use their email.
Step 1: In the address bar visit http://webmail.YourDomainName.com (so if your domain is joestaxes.com, go to https://webmail.joestaxes.com)
Step 2: Type in the username and password of the email that you wish to log in to (NOTE: Your username is the first half of your email address. So, if your email address is jim@joestaxes.com, just type in jim as the username).