Overview
After taking necessary action on an open conversation, such as sending a reply, leaving a note, or reading the newest message, you can close it. The conversation will then be moved to the "Closed" tab of your inbox, where you can easily reference or reopen it if needed.
If there is new activity in a closed conversation, the conversation will automatically reopen and be moved from the "Closed" tab back to the "Open" tab of your inbox.
How to close a conversation?
To close a conversation, simply click the Mark as closed button at the top of the conversation.
If you close a conversation that belongs to an Office 365 mailbox, by default the emails of that conversation will be moved to the Archived folder in the associated mailbox.
Reopen conversations
To reopen a conversation, find the conversation in the "Closed" tab of your inbox (or use search to retrieve the closed conversation). Then, click the Reopen button at the top of the conversation to move it back to the "Open" tab of your inbox.