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email: Undelivered Mail Returned to Sender #1802

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email: Undelivered Mail Returned to Sender#1802
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Description

@cheggerdev
cheggerdev
opened on Jul 10, 2026

Support guidelines

I've found a bug and checked that ...

  • ... the documentation does not mention anything about my problem
  • ... there are no open or closed issues that are related to my problem

Description

My diun docker configuration via environment variables is this:

DIUN_NOTIF_MAIL_HOST=<mailserver>
DIUN_NOTIF_MAIL_PORT=465
DIUN_NOTIF_MAIL_SSL=true
DIUN_NOTIF_MAIL_USERNAME=<user>
DIUN_NOTIF_MAIL_PASSWORD=<secret>
DIUN_NOTIF_MAIL_FROM=<sender-address>
DIUN_NOTIF_MAIL_TO=<receiver>

I do receive the expected email from the given mailserver above.
However, I additionally receive another mail subject "Undelivered Mail Returned to Sender" from an apple mailserver I do not specify:

The mail system

[<dev000h@icloud.com>](mailto:dev000h@icloud.com): host mx02.mail.icloud.com[17.57.154.33] said: 554 5.7.1
    [CS01] Message rejected due to local policy. Please visit
    https://support.apple.com/en-us/HT204137. Txn ID
    e32415fb-757b-48ae-8bb2-0d1399b4fe78 (in reply to end of DATA command)

[<dev000x@icloud.com>](mailto:dev000x@icloud.com): host mx02.mail.icloud.com[17.57.154.33] said: 554 5.7.1
    [CS01] Message rejected due to local policy. Please visit
    https://support.apple.com/en-us/HT204137. Txn ID
    e32415fb-757b-48ae-8bb2-0d1399b4fe78 (in reply to end of DATA command)

I have no idea why diun sends another email to an apple mailserver.
This new behaviour started to happen in June 21st.

Expected behaviour

I want the one expected email only.
I do want any unspecified actions in the background.

Actual behaviour

I do receive the expected emails.
Since June 21st I receive "Undelivered Mail Returned to Sender" from Apple Mailservers.

Nothing changed when it started on June 21st.
Other docker services also send emails but diun is the only one with this behaviour.

Steps to reproduce

sudo docker-compose exec -it diun diun notif test

Diun version

v4.33.0

Docker info

Client:
 Version:    24.0.2
 Context:    default
 Debug Mode: false
 Plugins:
  compose: Docker Compose (Docker Inc.)
    Version:  v2.20.1-6047-g6817716
    Path:     /usr/local/lib/docker/cli-plugins/docker-compose

Server:
 Containers: 26
  Running: 24
  Paused: 0
  Stopped: 2
 Images: 33
 Server Version: 24.0.2
 Storage Driver: btrfs
  Btrfs: 
 Logging Driver: db
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs db fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: fea6458b8abe502f6228eab2e5a6678fcb5c3fb0
 runc version: 0320c58
 init version: ed96d00
 Security Options:
  apparmor
 Kernel Version: 4.4.302+
 Operating System: Synology NAS

 OSType: linux
 Architecture: x86_64
 CPUs: 4
 Total Memory: 31.32GiB
 Name: nas-server
 ID: 8ae25fa6-7dd7-4ef5-93db-ca0ca04408ce
 Docker Root Dir: /volume1/@docker
 Debug Mode: false
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: No kernel memory TCP limit support
WARNING: No cpu cfs quota support
WARNING: No cpu cfs period support
WARNING: No blkio throttle.read_bps_device support
WARNING: No blkio throttle.write_bps_device support
WARNING: No blkio throttle.read_iops_device support
WARNING: No blkio throttle.write_iops_device support

Docker Compose config

name: diun
services:
  diun:
    command:
    - serve
    container_name: diun
    environment:
      DIUN_NOTIF_MAIL_FROM: <sender-address>
      DIUN_NOTIF_MAIL_HOST: <mailserver>
      DIUN_NOTIF_MAIL_PASSWORD: <password>
      DIUN_NOTIF_MAIL_PORT: "465"
      DIUN_NOTIF_MAIL_SSL: "true"
      DIUN_NOTIF_MAIL_TEMPLATEBODY: '{{ .Entry.Image.Path }} {{ if (eq .Entry.Status
        "new") }}created{{ else }}updated{{ end }} on {{ .Entry.Manifest.Created.Format
        "2006-02-02 15:04" }}'
      DIUN_NOTIF_MAIL_TEMPLATETITLE: '{{ .Entry.Image }} {{ if (eq .Entry.Status "new")
        }}is available{{ else }}has been updated{{ end }}'
      DIUN_NOTIF_MAIL_TO: <receipient>
      DIUN_NOTIF_MAIL_USERNAME: mail
      DIUN_PROVIDERS_DOCKER: "true"
      DIUN_PROVIDERS_DOCKER_WATCHBYDEFAULT: "true"
      DIUN_ROOT: /volume1/docker/diun
      DIUN_WATCH_JITTER: 30s
      DIUN_WATCH_SCHEDULE: 0 */12 * * *
      DIUN_WATCH_WORKERS: "20"
      DOCKER_ROOT: /volume1/docker
      LOG_JSON: "false"
      LOG_LEVEL: debug
      TZ: Europe/Berlin
    image: crazymax/diun:latest
    networks:
      default: null
    restart: unless-stopped
    volumes:
    - type: bind
      source: /volume1/docker/diun/data
      target: /data
      bind:
        create_host_path: true
    - type: bind
      source: /var/run/docker.sock
      target: /var/run/docker.sock
      bind:
        create_host_path: true
networks:
  default:
    name: diun_default
    driver: bridge

Logs

diun  | Fri, 10 Jul 2026 00:00:18 CEST INF Image update found image=docker.io/zabbix/zabbix-agent:alpine-7.4-latest provider=docker
diun  | Fri, 10 Jul 2026 00:00:18 CEST INF Image update found image=docker.io/zabbix/zabbix-server-pgsql:alpine-7.4-latest provider=docker
diun  | Fri, 10 Jul 2026 00:00:18 CEST INF Image update found image=docker.io/zabbix/zabbix-web-nginx-pgsql:alpine-7.4-latest provider=docker
diun  | Fri, 10 Jul 2026 00:00:18 CEST INF Image update found image=docker.io/zabbix/zabbix-snmptraps:alpine-7.4-latest provider=docker
diun  | Fri, 10 Jul 2026 00:00:19 CEST DBG Manifest saved to database image=docker.io/guacamole/guacd:1.6.0 provider=docker
diun  | Fri, 10 Jul 2026 00:00:19 CEST DBG No changes image=ghcr.io/goauthentik/radius:2026.5.3 provider=docker
diun  | Fri, 10 Jul 2026 00:00:20 CEST DBG No changes image=ghcr.io/goauthentik/ldap:2026.5.3 provider=docker
diun  | Fri, 10 Jul 2026 00:00:21 CEST DBG Manifest saved to database image=docker.io/crazymax/diun:latest provider=docker
diun  | Fri, 10 Jul 2026 00:00:23 CEST DBG Manifest saved to database image=docker.io/guacamole/guacamole:1.6.0 provider=docker
diun  | Fri, 10 Jul 2026 00:00:25 CEST DBG Manifest saved to database image=docker.io/dpage/pgadmin4:9.16 provider=docker
diun  | Fri, 10 Jul 2026 00:00:26 CEST DBG Manifest saved to database image=docker.io/portainer/portainer-ce:lts provider=docker
diun  | Fri, 10 Jul 2026 00:00:28 CEST DBG Manifest saved to database image=docker.io/bbernhard/signal-cli-rest-api:latest provider=docker
diun  | Fri, 10 Jul 2026 00:00:29 CEST DBG Manifest saved to database image=docker.io/freeradius/freeradius-server:3.2.10-alpine provider=docker
diun  | Fri, 10 Jul 2026 00:00:31 CEST DBG Manifest saved to database image=docker.io/linuxserver/dokuwiki:amd64-version-2025-05-14b provider=docker
diun  | Fri, 10 Jul 2026 00:00:33 CEST DBG Manifest saved to database image=docker.io/linuxserver/dokuwiki:amd64-version-2025-05-14b provider=docker
diun  | Fri, 10 Jul 2026 00:00:34 CEST DBG Manifest saved to database image=docker.io/mpepping/cyberchef:latest provider=docker
diun  | Fri, 10 Jul 2026 00:00:36 CEST DBG Manifest saved to database image=docker.io/linuxserver/dokuwiki:amd64-version-2025-05-14b provider=docker
diun  | Fri, 10 Jul 2026 00:00:37 CEST DBG Manifest saved to database image=ghcr.io/goauthentik/server:2026.5.3 provider=docker
diun  | Fri, 10 Jul 2026 00:00:39 CEST DBG Manifest saved to database image=ghcr.io/goauthentik/rac:2026.5.3 provider=docker
diun  | Fri, 10 Jul 2026 00:00:40 CEST DBG Manifest saved to database image=ghcr.io/goauthentik/server:2026.5.3 provider=docker
diun  | Fri, 10 Jul 2026 00:00:43 CEST DBG Manifest saved to database image=docker.io/zabbix/zabbix-agent:alpine-7.4-latest provider=docker
diun  | Fri, 10 Jul 2026 00:00:43 CEST DBG Sending mail notification... image=docker.io/zabbix/zabbix-agent:alpine-7.4-latest
diun  | Fri, 10 Jul 2026 00:00:45 CEST DBG Manifest saved to database image=docker.io/zabbix/zabbix-server-pgsql:alpine-7.4-latest provider=docker
diun  | Fri, 10 Jul 2026 00:00:45 CEST DBG Sending mail notification... image=docker.io/zabbix/zabbix-server-pgsql:alpine-7.4-latest
diun  | Fri, 10 Jul 2026 00:00:48 CEST DBG Manifest saved to database image=docker.io/zabbix/zabbix-web-nginx-pgsql:alpine-7.4-latest provider=docker
diun  | Fri, 10 Jul 2026 00:00:48 CEST DBG Sending mail notification... image=docker.io/zabbix/zabbix-web-nginx-pgsql:alpine-7.4-latest
diun  | Fri, 10 Jul 2026 00:00:50 CEST DBG Manifest saved to database image=docker.io/zabbix/zabbix-snmptraps:alpine-7.4-latest provider=docker
diun  | Fri, 10 Jul 2026 00:00:50 CEST DBG Sending mail notification... image=docker.io/zabbix/zabbix-snmptraps:alpine-7.4-latest
diun  | Fri, 10 Jul 2026 00:00:52 CEST DBG Manifest saved to database image=ghcr.io/goauthentik/radius:2026.5.3 provider=docker
diun  | Fri, 10 Jul 2026 00:00:54 CEST DBG Manifest saved to database image=ghcr.io/goauthentik/ldap:2026.5.3 provider=docker
diun  | Fri, 10 Jul 2026 00:00:54 CEST INF Jobs completed added=0 failed=0 skipped=0 unchanged=16 updated=4
diun  | Fri, 10 Jul 2026 00:00:54 CEST INF Next run in 12 hours (2026-07-10 12:00:29.723864004 +0200 CEST)

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