Our Hosted Exchange services allows mailboxes to have multiple email addresses attributed to them. One email address will be setup as primary, and will be used in all replies.
For example, if your user John had the primary email address "email@example.com", and also had "firstname.lastname@example.org" setup as an additional email address, any email sent to the sales address will arrive in John's mailbox. If John replies to the email, the reply will be sent from "email@example.com".
To setup an additional email address, login to the control panel and select Exchange from the top menu.
Find the mailbox you wish to add an additional address to and select E-mail addresses. All current email addresses attributed to that mailbox will be displayed. Click Add New E-mail Address to add another.
On the next page you'll be asked for the email address you wish to add. Click Submit when done. Your additional email address will be added to the list.
If you wish to change the primary email address for the mailbox, then please read this article.