Hello,
Thank you for reaching out to the community. We actually have a setting that is perfect for this.
In the domain configuration, you can set inbound message delivery to External use MX record and then turn on Deliver locally if the user exists. This should make it so when
user2@example.com(On SmarterMail) tries to send to
user1@example.com(On Exchange) it will check locally then if the user doesn't exist it will send it out to the exchange server using the MX record.
Please let me know if this helps.
Kind Regards,
Zach Sylvester
System/Network Administrator
SmarterTools Inc.
(877) 357-6278
www.smartertools.com