You can configure settings related to forums in Settings -> Community -> Forums.
Send forum e-mails from
Sets the e-mail address that will be used as the sender for forum notifications and confirmation e-mails.
Forum base URL
This setting should contain the relative URL of the page where the website's forums are located, for example:
Forum groups and individual forums can either inherit this value from the settings or use their own. Having a correct base URL is important for generating valid links in forum-related e-mails.
Forum attachments allowed extensions
Allows you to specify a list of file extensions that will be allowed for forum post attachments. The extensions should be entered without dots and separated by semicolons. If blank, all extensions are allowed.
Max forum post nodes
Determines the maximum number of forum post nodes displayed in the forum post tree when editing a forum in the Forums application.
If there are more nodes than allowed by this value, the click here for more ... link will be displayed at the bottom of the tree, letting you display a list of all nodes in the main area.
Forum unsubscription URL
Sets the URL of the page that unsubscribes users from receiving notifications about new forum posts. The Forum unsubscription web part must be placed on the page in order for the unsubscriptions to work.
The value of this setting can be inherited by forum groups and through them by particular child forums. If left empty, the ~/CMSPages/Unsubscribe.aspx default page is used.
Enable double opt-in for forums
Indicates if double opt-in should be enabled for forum objects. 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 Forum 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 user after they approve a subscription. If double opt-in is disabled, these confirmation e-mails are always sent.