Mark as shared

compose.mailman.yml

@@ -3,13 +3,13 @@ version: "3.6"
 services:
   smtp:
     volumes:
-      - "mailman-core:/opt/mailman/"
+      - "shared-mailman-core:/opt/mailman/"
     configs:
       - source: postfix_override
         target: /overrides/postfix.cf
 
 volumes:
-  mailman-core:
+  shared-mailman-core:
     # https://git.autonomic.zone/coop-cloud/mailman3/src/branch/master/compose.yml
     external: true
     name: ${MAILMAN_CORE_VOLUME}