EシリーズのPSU障害アラートが送信されませんでした

Web server trace log:

2023-08-01 14:12:36,185 INFO [ActiveMQ Session Task-3431] s.p.AlertManagerService [AlertManagerService.java:437] [requestId=0, deviceId=N/A] Notification from peer, reloading Alert configuration
2023-08-01 14:12:36,187 INFO [jetty-12357] trace [AlertConfigurationServiceImpl.java:228] [requestId=1d4ef61d-f29c-4879-bbc3-9748701d6fcb, deviceId=1] Updating Alert Configuration data
…
2023-08-01 14:12:56,397 ERROR [ActiveMQ Session Task-3431] s.p.AlertManagerService [AlertManagerService.java:278] [requestId=0, deviceId=N/A] Mail server cannot be found: smtp-relay.gmail.com
Caller+0 at smmonitor.persistentmonitor.AlertManagerService.readGlobalConfiguration(AlertManagerService.java:278)
Caller+1 at smmonitor.persistentmonitor.AlertManagerService.onMessage(AlertManagerService.java:441)
Caller+2 at org.apache.activemq.ActiveMQMessageConsumer.dispatch(ActiveMQMessageConsumer.java:1433)
Caller+3 at org.apache.activemq.ActiveMQSessionExecutor.dispatch(ActiveMQSessionExecutor.java:131)
Caller+4 at org.apache.activemq.ActiveMQSessionExecutor.iterate(ActiveMQSessionExecutor.java:202)
java.net.UnknownHostException: smtp-relay.gmail.com: Temporary failure in name resolution