diff --git a/src/data/collection.mjs b/src/data/collection.mjs
index 85d3e76..2af9fb3 100644
--- a/src/data/collection.mjs
+++ b/src/data/collection.mjs
@@ -452,17 +452,24 @@ export const collected = [
       'operator can see what was suppressed without the list becoming a second address ' +
       'book.',
     retention: {
-      summary: 'Kept until the operator removes them; nothing here expires on its own',
+      summary:
+        'The delivery log is kept for a period the operator sets (180 days by default) and then ' +
+        'swept; the suppression list does not expire',
       detail:
-        'Stated plainly because it is the answer people assume the other way round: ' +
-        'the delivery log, the suppression list and the per-person rate limits have no ' +
-        'retention sweep, so they are as long as the site is old. Deleting an account ' +
-        'detaches its rows from it rather than deleting them — a delivery history stops ' +
-        'naming a person, and a suppressed address stays suppressed.',
+        'A nightly sweep removes delivery-log entries, finished items from the send queue and the ' +
+        'per-person rate-limit rows once they pass the horizon the operator has set for each — ' +
+        'the defaults are 180 days for the log and 30 for the other two. Two things deliberately ' +
+        'do not expire. An item still waiting to be sent is never swept however old it is, ' +
+        'because it is a message the site still intends to deliver. And the suppression list is ' +
+        'permanent by design: it records a standing decision to stop mailing an address, and ' +
+        'ageing an entry out would mean mailing an address that already bounced or asked to be ' +
+        'left alone. An operator can remove an entry from it deliberately, one at a time. ' +
+        'Deleting an account detaches its rows from it rather than deleting them — a delivery ' +
+        'history stops naming a person, and a suppressed address stays suppressed.',
     },
     source:
       'website server/db/schema.sql — engagement_sends, engagement_suppressions, ' +
-      'notification_channel_prefs',
+      'notification_channel_prefs; server/src/utils/engagementRetentionPrune.js',
   },
   {
     id: 'deploy-game-data',