This is the (hopefully) last split from bug 28026.
This preference is not true by default in our config, nor in the default MediaWiki config, which doesn't make much sense; I checked inspired by something jdforrester wrote me: «I assumed that when I created an account "e-mail me about pages I watch" was switched on, as per most other instances nowadays». They should indeed!
So, the plan is still the same as in bug 28026 comment 60 by Roan, except that $wgEnotifWatchlist is currently true:
# Add (or hack in) a MW config var that makes it so the enotifwatchlistpages preference is visible, but not functional (i.e. enabling it doesn't actually cause e-mails to be sent). This will stop watchlist e-mail notifs (similar to disabling $wgEnotifWatchlist) but preserve the preference.
# Enable this config var.
# Compile a list of users that have the preference enabled.
# Set $wgDefaultUserOptions['enotifwatchlistpages'] = 1; . The preference is now enabled for all users, but because it's not functional, there is no deluge of e-mail notifications overwhelming our mail system.
# Using a maintenance script, set the preference to 0 for each userindividually, excluding users that already had it enabled (from the list madein step 3) and invalidating the user cache for each user that it touches. Running this will probably take a while (a few hours?) on a large wiki like enwiki.
# Undo step 2 (disable the config var). The preference is now functional again and enabled for the same set of users, but it will now also be enabled by default for new users
This seemed to be harder than bug 36316 as first step, but unlike bug 36316 it can't possibly give any problem with bots as long as their watchlists are empty, and it won't affect existing users (or whatever subset of them we choose) thanks to the maintenance script.
New users will still have to manually enable enotifwatchlist but won't have to understand the watchlist before starting to use it...
**See Also**: https://bugzilla.wikimedia.org/show_bug.cgi?id=45022