You can configure settings related to message boards in Settings -> Community -> Message boards.
Send message board e-mails from
E-mail address that will appear in the From field of notification messages about new message board messages.
Board base URL
Global board base URL that can be inherited by message boards. It can be used by board notification e-mails and message board viewers.
Board unsubscription URL
URL of the site on that the Message board unsubscription web part is placed. This web part handles requests for unsubscription from notifications about new message board messages.
Enable double opt-in for message boards
Indicates if double opt-in should be enabled for message boards. When enabled, users are required to confirm their subscription by clicking a link that is sent to them in an e-mail.
You can override this setting in the properties of a particular forum group or a forum.
Double opt-in approval page path
Path to the page that contains the Message board subscription confirmation web part. The subscription confirmation link that will be sent to users will point to this page.
Double opt-in interval (hours)
Amount of time in hours, during which a user has to confirm their subscription request.
Send double opt-in confirmation
Indicates if an e-mail confirmation should be sent to users after they approve a subscription. If double opt-in is disabled, these confirmation e-mails are always sent.