Is there a way to enable the VRFY command on the Exchange server. I know this command is a security risk, but the server sits behind a firewall, and is not accessible from the internet. I would just use it as a in-box. The mail traffic would be forwarded from my home coded SMTP server, which would check for the existence of the exchange mailbox with the VRFY command.
I only found this on the internet, but this is only for legacy versions of Exhange.