Multiple Addresses for Private Users
As a private user, multiple eMail addresses can serve a number of purposes:

Business Partners or Groups
An eMail plan with multiple addresses allows you to create separate eMail addresses for each of your business partner or any other group of users.

Multiple Mailboxes
Private eMail users may want to set up separate mailboxes for specific purposes. For example, mailboxes dedicated to personal mail, work-related mail, Website related mail, etc.

An account with multiple addresses can cover all such needs.

Multiple Addresses for Business Users
As a business owner, there are several ways you can take advantage of multiple mailboxes:

eMail addresses for employees
If your business has a staff, then each staff member needs his/her own mailbox. Providing your employees with individual mailboxes on your domain (rather than generic addresses, such as Hotmail®, Yahoo!Mail®, etc.) is not only convenient for the employees; it shows the world that you are serious about your business.

Separate eMail addresses for product lines, offerings, etc.
If you are running a multi-tiered business, such as an e-commerce business that offers a variety of product types or lines, you might want to set up separate mailboxes for communications within each distinct section of your business.