A mail sent with rewards will be stored in the mailbox for 60 days.

An announcement mail that is about a current event will be stored for 15 days.

You can claim the rewards anytime you want within 60 days. You can choose to delete the mail after you have claimed the rewards or read the announcement, or leave it to be automatically deleted after the due date. If you forget to claim your rewards after 60 days, the mails with them will be automatically deleted without providing you with the rewards.