Are you trying to set up web based e-mail for visitors, or mailbox services for yourself/friends/family?
If it's web-based e-mail, you'll need to ask your web provider if it does not violate your terms of service with them.
It it's mailbox services, the web provider should allocate a number of mailboxes and virtual (redirecting) mail services. Without knowing who you're going through, those numbers vary all over the scale.
Also, there are two types of mailboxes you can set up for the employees. Your web host may restrict how many boxes you have available, so this is important.
Real mailboxes (firstname.lastname@example.org, mail server is mail.domain.com for SMTP and POP3) - For these there are usually a limited number, and you have to set up the mail client to look to a different server.
Virtual mailboxes (email@example.com forwards to your normal e-mail) - Some servers restrict the number of accounts you can have. The big difference is on the client side. With a virtual e-mail you set up everything to look at your usual e-mail address.
As jonese said, check with your provider. They have final say as to what you can and cannot do. For setting up the actual accounts, most providers have a site control panel that will have e-mail setups for it.