Administrators and Moderators can subscribe to campaign with the purpose of receiving notification for new ideas and comments.
Subscribing to Campaign allows the subscriber to receive notification for all the new ideas and comments for the only campaign subscribed.
Steps to subscribe/ unsubscribe campaign.
 1) Click on the desired campaign. You will see "Subscribe to campaign" link just below the Campaign Question / Challenge Statement . Click on this link to enable idea/comment notification for a specific campaign.

2) Subscribe campaign is like toggle switch .Once the Administrator / Moderators subscribes to a campaign, they would see the option to "Unsubscribe". Click on unsubscribe link to stop idea/comment notification for a particular campaign.

Administrator has ability to provide or hide subscribe campaign link from user. This option can be set from
Community settings>>Basic settings>Manage campaigns.

Help article on campaign settings:

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