Available in: Group, Professional, Enterprise, Performance, Unlimited, Contact Manager, and Developer Editions
Chatter Messenger is not available in new orgs created after the Spring ’16 release.
When you start a chat with someone, your conversations with them from the last 72 hours are automatically shown. Conversations older than 72 hours are deleted and can’t be retrieved. To see a list of all conversations from the last 72 hours:
Click the Chat header to expand the chat window.
Click someone’s name to see your chat history with them.