diff --git a/docker/diun/compose.yaml b/docker/diun/compose.yaml
index da41aa4..01188e6 100644
--- a/docker/diun/compose.yaml
+++ b/docker/diun/compose.yaml
@@ -11,6 +11,7 @@ services:
     volumes:
       - "./data:/data"
       - "./diun.yml:/diun.yml:ro"
+      - "./diun.list.yml:/diun.list.yml:ro"
       - "/var/run/docker.sock:/var/run/docker.sock"
     environment:
       - "TZ=America/New_York"
diff --git a/docker/diun/diun.list.yml b/docker/diun/diun.list.yml
new file mode 100644
index 0000000..68fb0c8
--- /dev/null
+++ b/docker/diun/diun.list.yml
@@ -0,0 +1,9 @@
+# Base images for locally-built containers. The docker provider doesn't see
+# these because the built image has a local-only tag. ctn_names metadata is set
+# so the email subject still points at the compose dir that needs rebuilding.
+- name: nextcloud:latest
+  metadata:
+    ctn_names: nextcloud-base
+- name: githubyumao/mcsmanager-daemon:latest
+  metadata:
+    ctn_names: mcsmanager-daemon-base
diff --git a/docker/diun/diun.yml b/docker/diun/diun.yml
index 084b04a..2fdc586 100644
--- a/docker/diun/diun.yml
+++ b/docker/diun/diun.yml
@@ -8,6 +8,11 @@ providers:
   docker:
     watchByDefault: true      # watch every running container without needing labels
     watchStopped: false
+  file:
+    # Explicit watches for base images of locally-built containers (apps with a
+    # Dockerfile in their compose dir). The docker provider can't see these
+    # because the built image has a local-only tag with no registry digest.
+    filename: /diun.list.yml
 
 notif:
   mail:
@@ -19,4 +24,13 @@ notif:
     from: argento@fastmail.com
     to:
       - timothykim@fastmail.fm
+    # Subject leads with container name so the compose dir is obvious from the inbox
+    # (e.g. "nextcloud-redis" -> docker/nextcloud/). Default template uses the full
+    # canonical ref with @sha256 digest, which is unreadable.
+    templateTitle: '[{{ .Entry.Status }}] {{ .Entry.Metadata.ctn_names }} ({{ .Entry.Image.Path }}:{{ .Entry.Image.Tag }})'
+    templateBody: |
+      Container: {{ .Entry.Metadata.ctn_names }}
+      Image:     {{ .Entry.Image.Path }}:{{ .Entry.Image.Tag }}
+      {{ if .Entry.Image.HubLink }}Link:      {{ .Entry.Image.HubLink }}{{ end }}
+      Host:      {{ .Meta.Hostname }}