diff --git a/data/settings.js b/data/settings.js
index bb7bc69f4..474e84454 100644
--- a/data/settings.js
+++ b/data/settings.js
@@ -7344,6 +7344,11 @@ See [[link,mail_cache]] for details and for the list of fields.`
 
 	mail_attachment_detection_options: {
 		values: setting_types.BOOLLIST,
+		default: `
+add-flags "content-type=!application/signature"
+<br /><br />
+[[changed,mail_attachment_detection_options_changed]] The default value was
+added. It used to be empty.`,
 		text: `
 Settings to control adding \`$HasAttachment\` or \`$HasNoAttachment\`
 keywords. By default, all MIME parts with \`Content-Disposition=attachment\`
diff --git a/data/updates.js b/data/updates.js
index f5f6dc8e1..b9af157f3 100644
--- a/data/updates.js
+++ b/data/updates.js
@@ -51,6 +51,7 @@ export const updates = {
 	lua_auth_init: '2.4.0',
 	lua_dns_client: '2.4.0',
 	lua_script_init: '2.4.0',
+	mail_attachment_detection_options_changed: '2.4.2',
 	mail_cache_fields_changed: '2.4.1',
 	mail_crypt_eddsa: '2.4.0',
 	mail_crypt_fs_maybe: '2.4.0',
diff --git a/docs/installation/upgrade/2.4-to-2.4.x.md b/docs/installation/upgrade/2.4-to-2.4.x.md
index fdc8cb918..902e18ac2 100644
--- a/docs/installation/upgrade/2.4-to-2.4.x.md
+++ b/docs/installation/upgrade/2.4-to-2.4.x.md
@@ -26,3 +26,16 @@ changed from `2.4.0` to `2.4.1`.
 | `service/auth/unix_listener/auth-userdb/group` | (empty = root) | `$SET:default_internal_group` |
 | `service/lmtp/restart_request_count` | unlimited | 1 |
 | [[setting,lmtp_user_concurrency_limit]] | unlimited | 10 |
+
+### v2.4.1 to v2.4.2
+
+#### Changed Setting Defaults
+
+These changes don't take effect until [[setting,dovecot_config_version]] is
+changed to `2.4.2`.
+
+| Setting | Old Default Value | New Default Value |
+| ------- | ----------------- | ----------------- |
+| [[setting,mail_attachment_detection_options]] |  | `add-flags content-type=!application/signature` | |
+| `service/anvil/unix_listener/anvil/mode` | `0600` | `0660` |
+| `service/anvil/unix_listener/anvil/group` | (empty = root) | `$SET:default_internal_group` |