My Server stop send and receive emails after Plesk Obsidian 18.0.68 Update 1

All the mails in the queue are stuck as deferred

Summary status​

4.3.2 deferred (host 127.0.0.1[127.0.0.1] said: 421 4.3.2 Service shutting down, closing channel (in reply to RCPT TO command))

Please help!