Outlook / Exchange 2007 mail redirect

Hi all--
I am hunting for an elegant solution to a mail redirect problem.  Here's the layout:
Server is SBS 2008 (running Exchange 2007 SP1).
Client is XP SP3 with Outlook 2007 SP3.

My customer has a generic e-mail account.  Let's call it info@domain.com.  Info@domain.com is setup as a user, complete with Exchange mailbox, on the SBS server.  A receptionist at the company monitors the e-mail box and then either replies directly to the sender or forwards the message to the applicable user with the company.

The problem I am having is with forwarding of messages.  Rather than forwarding the messages, the receptionist would like to redirect them.  Using redirect, the original e-mail address is preserved.  As an example:
1.  Mail is sent from user@gmail.com to info@domain.com.
2.  Receptionist forwards the message from the info@domain.com mailbox to becky@domain.com.
3.  When Becky receives the message, it shows as being from info@domain.com.  We would like to preserve the original e-mail sender.  In maintaining the original address, Becky does not have to copy/paste the address from the body of the e-mail.

Possible solutions I have investigated:
1.  Seeing as Outlook 2007 does not seem to have a native redirect function, I tried re-sending of the message.  (Open message in Outlook, Select Other Actions, Resend This Message).

2.  Tried setting up account in Thunderbird 2.x via POP/SMTP. Downloaded and installed mail redirect add-in for Thunderbird 2.x (add-in doesn't work with TB 3.x) Configured POP/SMTP settings to my Exchange 2007 server.  Able to receive / send / forward successfully.  When I try redirect, receive the following:

An error occurred while sending mail.  The mail server responded 5.7.1 Client does not have permissions to send as this sender.  Please check the message and try again.

I have tried tweaking Send As permissions, delegating access, etc. to no effect.

Either Outlook or TBird solution is fine by me.

Thanks