Change General preferences in Messages on Mac
In the Messages app on your Mac, use General preferences to change general options for using Messages.
To change these preferences, choose Messages > Preferences, then click General.
Set Up Name and Photo Sharing
Set up name and photo sharing to share your name and photo with the people you choose.
Update your first and last name (only available after you set up name and photo sharing).
Share Name and Photo
Share your name and photo in the messages you send. Deselect the option to stop sharing your name and photo (only available after you set up name and photo sharing).
Share your name and photo with only your contacts or have Messages prompt you before your name and photo are shared in a new conversation (only available after you set up name and photo sharing).
Choose how long to keep message conversations in your account. For example, if you choose 30 Days, your conversations (and all attachments) are available in Messages for 30 days. After that, they are automatically removed.
Notify me about messages from unknown contacts
Receive a notification whenever anyone contacts you. If you don’t select this option, you get a notification only if you’re contacted by someone who is listed in Contacts or is someone you previously received messages from.
Notify me when my name is mentioned
Receive a notification whenever anyone mentions you in a conversation.
Auto-play message effects
Play full-screen effects automatically when received.
Play sound effects
Play the default sound effect when any event occurs. For more details, see Play sound effects.
Message received sound
Choose the sound that plays when a message is received.
Adjust the size of text in Messages.