root@carbonio:/var/log# /opt/zextras/common/sbin/postcat -q 4626B161A76

result:

root@carbonio:/var/log# /opt/zextras/common/sbin/postcat -q 4626B161A76
*** ENVELOPE RECORDS active/4626B161A76 ***
message_size:             698             337               1               0             698               0
content_filter: smtp-amavis::10024
message_arrival_time: Tue Sep 10 11:30:02 2024
create_time: Tue Sep 10 11:30:34 2024
named_attribute: rewrite_context=local
sender_fullname: CronDaemon
sender: zextras@pronet-info.com.tw
named_attribute: encoding=8bit
named_attribute: dsn_orig_rcpt=rfc822;zextras@pronet-info.com.tw
original_recipient: zextras
recipient: zextras@pronet-info.com.tw
*** MESSAGE CONTENTS active/4626B161A76 ***
Received: by carbonio.pronet-info.com.tw (Postfix, from userid 998)
        id 4626B161A76; Tue, 10 Sep 2024 11:30:02 +0800 (CST)
From: root@pronet-info.com.tw (Cron Daemon)
To: zextras@pronet-info.com.tw
Subject: Cron <zextras@carbonio> /opt/zextras/libexec/zmqueuelog
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
X-Cron-Env: <SHELL=/bin/bash>
X-Cron-Env: <HOME=/opt/zextras>
X-Cron-Env: <LOGNAME=zextras>
Message-Id: <20240910033034.4626B161A76@carbonio.pronet-info.com.tw>
Date: Tue, 10 Sep 2024 11:30:02 +0800 (CST)

postqueue: fatal: Queue report unavailable - mail system is down (Connect to the Postfix showq service: Connection refused)
*** HEADER EXTRACTED active/4626B161A76 ***
named_attribute: encoding=8bit
*** MESSAGE FILE END active/4626B161A76 ***

So I check the MTA service

root@carbonio:/var/log# sudo systemctl status carbonio-mta-sidecar.service
● carbonio-mta-sidecar.service - Carbonio mta sidecar proxy
     Loaded: loaded (/lib/systemd/system/carbonio-mta-sidecar.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2024-08-20 13:24:48 CST; 2 weeks 6 days ago
       Docs: https://docs.zextras.com/
   Main PID: 5104 (envoy)
      Tasks: 16 (limit: 19050)
     Memory: 16.3M
        CPU: 3h 15min 27.923s
     CGroup: /system.slice/carbonio-mta-sidecar.service
             └─5104 /usr/bin/envoy --config-path /tmp/envoy-17ed58745099dd56-bootstrap.json --disable-hot-restart

Sep 07 20:42:05 carbonio.pronet-info.com.tw consul:   cds:>Sep 07 20:42:05 carbonio.pronet-info.com.tw consul:   cds:>Sep 07 20:42:20 carbonio.pronet-info.com.tw consul:  [source/common/config/grpc_subscription_impl.cc:1>Sep 07 20:42:20 carbonio.pronet-info.com.tw consul:   lds: add/update list>Sep 10 04:53:03 carbonio.pronet-info.com.tw consul:   cds:>Sep 10 04:53:03 carbonio.pronet-info.com.tw consul:   cds:>Sep 10 04:53:18 carbonio.pronet-info.com.tw consul:  [source/common/config/grpc_subscription_impl.cc:1>Sep 10 04:53:18 carbonio.pronet-info.com.tw consul:   lds: add/update list>Notice: journal has been rotated since unit was started, output may be incomplete.

It seems to be normal, and I cannot find the cause. I hope you can help me.