From Exchange Server 2003 to Exchange 2010 SP2 (as of this writing) supports the ability to send email from different email addresses as long as the "send as" address has the same email address suffix of the users primary email address. For example I have an email address of firstname.lastname@example.org. Provided I have been granted permissions I can send as from different addresses such as email@example.com or firstname.lastname@example.org. However if my Exchange server has different Accepted Domains such as @kbomb.com.au I am not able to send as email@example.com even if I have been granted permissions. Doing so will result in the following error:
You can't send a message on behalf of this user unless you have permission to do so. Please make sure you're sending on behalf of the correct sender, or request the necessary permission. If the problem continues, please contact your helpdesk.
Microsoft's claims this functionality is "by design" and there is no intention to create a resolution at this stage.
There is a 3rd party tool called ChooseFrom which you install on your Exchange 2007/2010 server. This tool enables Send As functionality from different domains however its rather pricey. As of this writing the asking price was 286.46 USD for a 1-2 user license, $214.84 USD if you want over 3 licenses, $7161.50 USD for a site license or $30078.30 USD for an enterprise license in which they will also provide you with the source code. If you are interested in this tool please see the following website:
As an alternative you can create a new Outlook Profile and create a POP account. Outlook 2010 supports multiple profiles at the same time. In the address enter your Exchange 2010 hub transport server and configure SMTP authentication. In the POP3 server address enter something bogus like mail.local. Next you need to configure the send and receive group for your POP3 profile. To do this perform the following steps:
1. Under Send/Receive Groups select Define Send/Receive Groups.
2. Select your group name or define a new group and click Edit.
3. In the Send/Receive Settings disable Receive mail items.
Now when you send/receive you wont get an error about not being able to receive from the bogus pop server.