As at 25 October 2016, this feature has been disabled.
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When the feature is enabled, a 'Recommended Updates' email is automatically generated for users who have this enabled and is sent weekly, see example below. More details are available at https://confluence.atlassian.com/doc/configuring-the-recommended-updates-email-notification-281480712.html
If you are currently subscribed to receive the email, but would prefer not to, instructions on how to update your profile settings are available at https://confluence.atlassian.com/doc/email-notifications-145162.html