Having tested the mention notifications on test wiki, it should now be enabled on meta and mediawiki.org
Scheduled date: 2016-09-07
This task also includes deploying T140928: Find out if mention notifications are used
This task is based on a wish that received 21 points (#9) in the German Community Wishlist (T139962). Originally, the wish was to receive an information about the sent messages. To help people use mentions in a way that they are sent, we have also included notifications about mention failures, which add the reasons for the failure as well.