You can close any Conversation you belong to, even if you didn't create it. Closing a Conversation prevents people from adding new messages to it and removes it from people's list of Conversations.
To close a Conversation, click , then select Close Conversation.
To reopen a Conversation, from the navigation menu, select Conversations. In the Show menu, select Closed, then open the Conversation. Click , then select Reopen Conversation
You can discard a Conversation only if you're the sole member. A discarded Conversation is removed from all lists, including collections and Social Objects it's related to.
To discard a Conversation, click , then select Discard Conversation.
For more information, see How do I close, reopen, or discard an item?