Notifications provides a mechanism for automatic sending notices on defined action.
There are three kind of action.
1. Deadline minus defined time is reached (not implemented)
2. A new issue is submitted
3. A issue field is changed with optionally restricted old and new value

Notification can be sent by email or to users tray as a new item.
Of course user in client console can manual send a notification to any user tray.

This notification sends a mail to responsible person when it changes.

If you specifify such a mail text you can expect mails with bodies like:
You have been assigned to the issue ID=3 (first issue) by user2.

Notification supports these macros

<Field> inserts the Field caption
<ID> inserts the issue ID
<OldValue> inserts the old value
<NewValue> inserts the new value
<ChangedBy> inserts the user (editor) name
<ChangeAt> inserts the the time of change
<Field FieldName> inserts the value of the field FieldName