If a user has checked "Changes in issues assigned to me or reported by me", then he should be notified when new issues are automatically assigned to him.
Unlike the notification that is sent when a user makes a modification in the UI, we expect here to get only 1 notification with the link to the Issues page - whatever the number of issues have been assigned to the user.
For new issues assigned to someone, and if the option changed or modified by me is selected:
- how many issues were automatically assigned to you because you are the author
- the corresponding amount of technical debt that it represents
- and the direct link to the issues page
To sum up, an email similar to the general one for new issues (distribution by severity etc.)