Thread:Project:Support desk/How to enable email notification for watchlist changes by default/reply (3)

In that case you will be interested in $wgDefaultUserOptions.

$wgDefaultUserOptions['enotifwatchlistpages'] = true;

should be the option you are looking for. This will change the default for all new users and for all users, who have not customized their preferences. Existing user accounts who had the (previous) default option and didn't set it explicitly (which means that it's not stored in the database) will then use the new default.

For old users, who have changed the default, you can use the maintenance script userOptions.php to change their setting as well:

php userOptions.php enotifwatchlistpages --old 0 --new 1

This should change the value for those old users, who already have it in the DB = who changed from the default.