Multiple Domains

Exchange Gurus:

I have multiple accepted domains on Exchange 2010. The issue we see is that users can receive emails sent to any of the domains but they can only send email from their default Send-As domain. When they try to send-as one of the other secondary domains either nothing happens or they get an error saying they cannot send on behalf of this user....

I have users that work in multiple departments of the company and, at times, need their email address to reflect a specific domain. How can I do this without toggling the default reply domain in the user each time the need to send an email?

Thanks for any help!