After configuring Optional Destination Routing in Domain Settings, the email in Quarantine of SMG still cannot be released.
When click release in Quarantine of SMG, it shows error "Cannot release the message. It has either been released or was unable to contact the SMTP host."
The DNS in SMG Administration-->Hosts-->Configuration-->DNS/Time is public DNS server which didn't recognize private IP address. But the Mail Server A and B are using internal IP address.
Change the DNS server in SMG to an internal DNS server.
There are 1 SMG and 2 Mail Servers in the infrastructure. 8 domains are configured on SMG and Mail Servers. 3 domains are configured on Mail Server A. 5 domains are configured on Mail Server B. Message to different domains in quarantine should be routed to different Mail Server after release.
Optional Destination Routing in Domain Settings are configured and enabled to designate different domains to different IP of Mail Servers. Also the MX lookup in the local domain settings are not enabled.
SMG can send and receive email normally. But mails in Quarantine cannot be released.