If the SMTP server is configured on the control center with the setting " define new host " and the host IP address is for a scanner. Then we go and release a message from the quarantine, the message shows that it was released for a moment then it appears again in the quarantine. When looking in the Message Audit Logs, a new verdict and filter policy were added ( verdict: reinsert, Filter Policy: default ).
The message was quarantined in the first place because an "Email Malware Policy" was triggered.
This is an expected behavior.
The malware policies are always triggered on the messages even if they are coming from the quarantine. To avoid this scenario, change the SMTP settings in the control center to either "Use existing non-local relay settings" or to a host other than the scanners. (Administration > Settings > Control Center > SMTP)
For more details, please refer to Configure Control Center SMTP settings