Reproduction steps, on a fresh wiki with Jetty/hsqldb:
- Set grace time to 0 in xwiki.properties
- Configure the wiki to send email (from email address + email server) and set 0 to the time between emails
- Create a user with an email address
- Create a page "Page"
- Login with the user previously created
- enable all page notifications by alert and email
- enable mentions notifications by email (alert is already enabled by default)
- set email frequency to live
- Go to the page "Page"
- Unwatch the whole wiki with the watch buttons, and watch the current space
- Login again with Admin and create a new page "Sub page" under "Page" hierarchy
- a single mail is immediately received for the new page creation
- I immediately obtained 3 emails for same event
Note that performing further editions also lead to multiple emails.
The issue was originally reported on https://forum.xwiki.org/t/emails-are-sent-twice-or-three-times/13073 as impacting 14.10.15 but I reproduced it on 14.10.16.