ChooseFrom

Exchange mailbox may have multiple SMTP addresses. For outgoing messages Exchange server always uses the primary SMTP address. For example, John Doe has a mailbox with john.doe@companya.com primary SMTP address and john.doe@companyb.com secondary smtp address. John Doe can easily receive the message addressed both to john.doe@companya.com and john.doe@companyb.com, but he can not send the message as john.doe@companyb.com because this behaviour is by design in Exchange server.
ChooseFrom for Exchange 2000/2003 application allows users to send a message with any of their own SMTP addresses as the From address.