diff --git a/server/src/model/teams/teamNotify.model.js b/server/src/model/teams/teamNotify.model.js
index 168dd66..a085642 100644
--- a/server/src/model/teams/teamNotify.model.js
+++ b/server/src/model/teams/teamNotify.model.js
@@ -82,6 +82,24 @@ async function replacePrefs(userId, entries) {
     await db.setPref(userId, teamId, { muted: Boolean(entry.muted), emailMode })
     written.push(teamId)
   }
+
+  // A Team the caller COULD have named and did not is returned to its defaults.
+  //
+  // Without this, "replace the whole set" was a lie the endpoint told: omitting an
+  // entry left the old preference standing, which made `teams: []` — the body the
+  // route requires precisely so that clearing everything is expressible — clear
+  // nothing at all.
+  //
+  // Reset rather than deleted, and the difference is `last_digest_at`. That column
+  // is the digest worker's state, not a preference; dropping the row with it would
+  // make every visit to the settings screen re-open a day-wide digest window and
+  // mail somebody a summary they already read.
+  for (const teamId of allowed.keys()) {
+    if (written.includes(teamId)) continue
+    // eslint-disable-next-line no-await-in-loop
+    await db.setPref(userId, teamId, { muted: false, emailMode: 'off' })
+  }
+
   return { written, prefs: await listPrefs(userId) }
 }
 
diff --git a/server/test/teamNotify.test.js b/server/test/teamNotify.test.js
index 303d6aa..ccdea1c 100644
--- a/server/test/teamNotify.test.js
+++ b/server/test/teamNotify.test.js
@@ -214,6 +214,36 @@ test('replacePrefs ignores a Team the caller is not in', async () => {
   assert.equal(store.prefs.some((p) => p.user_id === 20 && p.team_id === 2), false)
 })
 
+test('replacePrefs really replaces: an omitted Team returns to its defaults', async () => {
+  await notifyModel.replacePrefs(10, [
+    { teamId: 1, muted: true, emailMode: 'immediate' },
+    { teamId: 2, muted: true, emailMode: 'digest' },
+  ])
+  // Now save a set that names only Team 1. Team 2 was not mentioned, so it goes
+  // back to defaults — otherwise "PUT the whole set" is a lie and `teams: []`
+  // clears nothing, which is the body the route requires so that clearing
+  // everything is expressible in the first place.
+  await notifyModel.replacePrefs(10, [{ teamId: 1, muted: true, emailMode: 'immediate' }])
+  assert.deepEqual(await notifyModel.prefFor(10, 1), { teamId: 1, muted: true, emailMode: 'immediate' })
+  assert.deepEqual(await notifyModel.prefFor(10, 2), { teamId: 2, muted: false, emailMode: 'off' })
+})
+
+test('an empty set clears every preference the caller holds', async () => {
+  await notifyModel.replacePrefs(10, [{ teamId: 1, muted: true, emailMode: 'digest' }])
+  await notifyModel.replacePrefs(10, [])
+  assert.equal((await notifyModel.prefFor(10, 1)).muted, false)
+  assert.equal((await notifyModel.recipientIds(1)).includes(10), true)
+})
+
+test('the reset does not touch last_digest_at — that is the worker’s column', async () => {
+  await notifyModel.replacePrefs(10, [{ teamId: 1, muted: false, emailMode: 'digest' }])
+  const row = store.prefs.find((p) => p.user_id === 10 && p.team_id === 1)
+  row.last_digest_at = '2026-08-18T00:00:00Z'
+  await notifyModel.replacePrefs(10, [])
+  assert.equal(row.last_digest_at, '2026-08-18T00:00:00Z',
+    'dropping it would re-open a day-wide window on every visit to the settings screen')
+})
+
 test('an unknown email mode falls back to off rather than reaching the column', async () => {
   await notifyModel.replacePrefs(10, [{ teamId: 1, muted: false, emailMode: 'hourly' }])
   assert.equal((await notifyModel.prefFor(10, 1)).emailMode, 'off')