Exchange mailbox may have multiple SMTP addresses. For outgoing messages Exchange always uses the primary SMTP address. For example, John Doe has a mailbox with firstname.lastname@example.org primary SMTP address and email@example.com secondary SMTP address. John Doe can easily receive the message addressed both to firstname.lastname@example.org and email@example.com, but he can not send the message as firstname.lastname@example.org because this behaviour is by design in Exchange server. ChooseFromOWA for Exchange 2003 application allows Outlook Web Access users to send message with any of their own SMTP addresses as the From address.
||Free to try
||Windows 2003 Server, Microsoft Exchange 2003