I'm doing testing, and slowly migrating specific users to open-xchange. So, I have firstname.lastname@example.org is still on my old email server.
If bob sends and email to tim, I'd like open-xchange forward the email to the old server. Basically, and unknown user should be forwarded. I was able to do this with Kolab, and I believe I only added/changed the following lines in /etc/postfix/main.cf
mydestination = dc1.domain.com
relayhost = 192.168.100.248
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 192.168.100.0
I get a 550 5.1.1 Recipient address rejected: User unknown in virtual mailbox table
The easiest setup would be to forward all unknown users in my local domain.com to another server.