Unsubscribe Topics 
To access the Unsubscribe panel, click the following: Threads & Posts > Unsubscribe.

On this page, you will be presented with two options for managing the thread subscriptions for your users.

Unsubscribe All Users from Specific Threads allows you to quickly remove all thread subscriptions from specific threads. Enter the thread IDs of the threads you wish to unsubscribe all users from; separate each with a space.

To obtain the thread ID, find the thread you want to remove. The link to the thread should look like http://www.example.com/forum_title/x-thread_title where forum_title is the forum title, thread_title is the thread title, and x is the thread ID you want. You would enter x into the form on this page. If there are multiple thread IDs, then separate them by spaces (not commas).

Unsubscribe All Threads from Specific Users allows you to quickly remove all of a user’s thread subscriptions. One reason you might do this is if the user’s email has been bouncing recently. However, this is not a temporary removal; you will not be able to restore the subscriptions in the future.

Here, you specify:
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