Do you want your Masto posts to self-destruct after a certain time period? Here's how to do it:

1. Log in through the website
2. Go to Preferences > Automated Post Deletion (on mobile you may need to click ☰ first)
3. Choose the Age Threshold to set how long posts are around before they’re deleted
4. Set the exceptions for posts you want to keep
5. Tick the box marked Automatically Delete Old Posts
6. Click the Save Changes button

To stop deletion, UN-tick the box and click Save Changes again.