The domain name portion of the recipient email address (for example, fortimail.example.com in release-ctrl@fortimail.example.com) could not be resolved by the DNS server into the FortiMail unit's IP address.
The sender's email address in the release message was not the same as the intended recipient of the email that was quarantined. If you have configured your mail client to handle multiple email accounts, verify that the release/delete message is being sent by the email address corresponding to that per-recipient quarantine. For example, if an email for user@example.com is quarantined, to release that email, you must send a release message from user@example.com.
