matrix: Update homeserver config from sample_config.yaml

roles/matrix/templates/homeserver.yaml.j2

@@ -375,11 +375,10 @@ retention:
     min_lifetime: 1d
     max_lifetime: 1y
 
-  # Retention policy limits. If set, a user won't be able to send a
-  # 'm.room.retention' event which features a 'min_lifetime' or a 'max_lifetime'
-  # that's not within this range. This is especially useful in closed federations,
-  # in which server admins can make sure every federating server applies the same
-  # rules.
+  # Retention policy limits. If set, and the state of a room contains a
+  # 'm.room.retention' event in its state which contains a 'min_lifetime' or a
+  # 'max_lifetime' that's out of these bounds, Synapse will cap the room's policy
+  # to these limits when running purge jobs.
   #
   allowed_lifetime_min: 1d
   allowed_lifetime_max: 1y
@@ -405,12 +404,19 @@ retention:
   # (e.g. every 12h), but not want that purge to be performed by a job that's
   # iterating over every room it knows, which could be heavy on the server.
   #
+  # If any purge job is configured, it is strongly recommended to have at least
+  # a single job with neither 'shortest_max_lifetime' nor 'longest_max_lifetime'
+  # set, or one job without 'shortest_max_lifetime' and one job without
+  # 'longest_max_lifetime' set. Otherwise some rooms might be ignored, even if
+  # 'allowed_lifetime_min' and 'allowed_lifetime_max' are set, because capping a
+  # room's policy to these values is done after the policies are retrieved from
+  # Synapse's database (which is done using the range specified in a purge job's
+  # configuration).
+  #
   purge_jobs:
-    - shortest_max_lifetime: 1d
-      longest_max_lifetime: 3d
+    - longest_max_lifetime: 3d
       interval: 12h
     - shortest_max_lifetime: 3d
-      longest_max_lifetime: 1y
       interval: 1d
 
 # Inhibits the /requestToken endpoints from returning an error that might leak
@@ -2003,9 +2009,7 @@ email:
   # Directory in which Synapse will try to find the template files below.
   # If not set, default templates from within the Synapse package will be used.
   #
-  # DO NOT UNCOMMENT THIS SETTING unless you want to customise the templates.
-  # If you *do* uncomment it, you will need to make sure that all the templates
-  # below are in the directory.
+  # Do not uncomment this setting unless you want to customise the templates.
   #
   # Synapse will look for the following templates in this directory:
   #