run filtermail as dedicated user

cmdeploy/src/cmdeploy/__init__.py

@@ -451,6 +451,7 @@ def deploy_chatmail(config_path: Path) -> None:
 
     server.group(name="Create vmail group", group="vmail", system=True)
     server.user(name="Create vmail user", user="vmail", group="vmail", system=True)
+    server.user(name="Create filtermail user", user="filtermail", system=True)
     server.group(name="Create opendkim group", group="opendkim", system=True)
     server.user(
         name="Create opendkim user",

cmdeploy/src/cmdeploy/service/filtermail.service.f

@@ -5,6 +5,7 @@ Description=Chatmail Postfix before queue filter
 ExecStart={execpath} {config_path}
 Restart=always
 RestartSec=30
+User=filtermail
 
 [Install]
 WantedBy=multi-user.target