After upgrading to ESG 5 and importing all configurations from ESG 4.9, quarantine reports and releases are not sent.
ESG before 4.9 allowed upload of certificate with incomplete certificate chains, which are invalid for almost any application but web clients.
Starting with ESG 5.0, TLS validation is strict for every service, so the application refuses to talk to the MTA due to the (now) invalid certificate imported.
This usually happens when using wildcard certificates.
Retrieve your certificate, eventually by logging into you Certification Authority panel, and download the certificates again. Then upload again the wildcard/standard certificate from the page “Admin Area > Appliance > TLS Certificates”, and override the configuration for the invalid one.