Save or delete text conversations in Messages on Mac
Messages saves your conversations, so even if you turn off your Mac or start using another device, you can pick up where you left off. You can set Messages to save a conversation or delete it when you close the conversation. If you set Messages to automatically save conversations, you can close a conversation and resume it later with the conversation history intact.
In the Messages app on your Mac, do any of the following:
Automatically save conversations: Choose Messages > Preferences, click General, then select “Save history when conversations are closed.”
Set how long to keep messages: Choose Messages > Preferences, click General, then click the “Keep messages” pop-up menu and choose an option.
Important: If you choose an option other than Forever, your conversations (including all attachments) are automatically removed after the specified time period is over.
Close a conversation: Move the pointer over the conversation, then click .
Note: If conversations are automatically saved, you can restore a closed conversation by composing a new text message to the individual or group.
Close all conversations: If conversations are automatically saved, press Option-Shift-Command-W.
Delete a conversation: Select a conversation, then choose File > Delete Conversation. Or, if you have a trackpad or a Magic Mouse, you can also swipe left with two fingers on the conversation in the sidebar, then click Delete.
If you use Messages in iCloud, deleting a conversation on your Mac deletes it from all of your devices where Messages in iCloud is turned on.
Clear all messages without closing a conversation: Choose Edit > Clear Transcript.