A temporary inbox is created for short-lived, low-trust tasks such as signup verification, testing, downloads, newsletters, and trials. It is not meant for banking, healthcare, legal notices, account recovery, or anything you must keep long term.
Message pages are treated differently from public content pages. They are not included in the sitemap, they are marked noindex, and the site layout disables ad placements on private mail routes.
For durable account access, use a permanent email address you control, a password manager, and two-factor authentication where available.