This is not possible in the currently released versions. However, v0.20.0 is released these days (Preview version are already available) that will allow you to do that.
Graylog2 Alarms for non admins
Question
How can unprivileged users subscribe to alarms?
Administrators see the alarm tab on each stream. It lets you subscribe in order to get an email if a message limit per timeframe is hit. For "readers" the tab is invisible.
Solution
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