The option "Email me when a page or file on my watchlist is changed" is hidden in a location that might have been logical to put it 10 years ago, but now isn't any more.
I wanted to enable email notification on some WMF wiki. I don't usually use that so I had to look
* I first looked at notifications. Lot's of stuff about notifications, also email options, but no option to enable watchlist notifications
* Second I looked under the watchlist tab. Plenty of boxes to tick, but no email box
* Third I clicked on the first tab ("user profile") to just go through all the tabs one by one. Luckily I found the option there
This isn't a very nice user interface experience. I don't have a ready made solution. I see two directions:
* Move the box somewhere else
* Duplicate the same option on multiple locations so users can find it in multiple ways
Probably best to have the user interface people have a look at this.