diff --git a/mailnews/mailnews.js b/mailnews/mailnews.js
index 2bb15c890e37..25eff8c8cab5 100644
--- a/mailnews/mailnews.js
+++ b/mailnews/mailnews.js
@@ -71,9 +71,9 @@ pref("mail.imap.upgrade.auto_subscribe_to_all",     false);
 pref("mail.imap.auto_unsubscribe_from_noselect_folders",    true);
 pref("mail.imap.allow_multiple_folder_connections",     false);
 pref("mail.imap.cleanup_inbox_on_exit",     false);
-pref("mail.imap.mime_parts_on_demand",      false);
+pref("mail.imap.mime_parts_on_demand",      true);
 pref("mail.imap.mime_parts_on_demand_max_depth", 15);
-pref("mail.imap.mime_parts_on_demand_threshold", 15000);
+pref("mail.imap.mime_parts_on_demand_threshold", 30000);
 pref("mail.imap.optimize_header_dl",        false);
 pref("mail.use_altmail",                    false);
 pref("mail.altmail_dll",                    "postal32.dll");
diff --git a/modules/libpref/src/init/mailnews.js b/modules/libpref/src/init/mailnews.js
index 2bb15c890e37..25eff8c8cab5 100644
--- a/modules/libpref/src/init/mailnews.js
+++ b/modules/libpref/src/init/mailnews.js
@@ -71,9 +71,9 @@ pref("mail.imap.upgrade.auto_subscribe_to_all",     false);
 pref("mail.imap.auto_unsubscribe_from_noselect_folders",    true);
 pref("mail.imap.allow_multiple_folder_connections",     false);
 pref("mail.imap.cleanup_inbox_on_exit",     false);
-pref("mail.imap.mime_parts_on_demand",      false);
+pref("mail.imap.mime_parts_on_demand",      true);
 pref("mail.imap.mime_parts_on_demand_max_depth", 15);
-pref("mail.imap.mime_parts_on_demand_threshold", 15000);
+pref("mail.imap.mime_parts_on_demand_threshold", 30000);
 pref("mail.imap.optimize_header_dl",        false);
 pref("mail.use_altmail",                    false);
 pref("mail.altmail_dll",                    "postal32.dll");