Manual:$wgEnotifUseJobQ

Details
Since MediaWiki 1.27, the job queue is always used to send email.

If true, send mails via the queue>Special:MyLanguage/Manual:Job queue|job queue.

If you are setting this value to true, check that  is set explicitly in your , as the usual $_SERVER method for detecting the wiki URL will not work if the job queue is run from a cron script.