mailbox.org recycles @mailbox.org addresses after a period. 90 days for the cheapest Light plan [1].

After that, someone else can register your old address.

If your subscription lapses, your email account is closed after 30 days, data is deleted after another 30 days [2].

[1]: https://kb.mailbox.org/en/private/account-article/when-is-a-...

[2]: https://kb.mailbox.org/en/private/payment-article/what-happe...