DEAD_LETTERS kept a message given up on MAIL forever and showed it whole to any caller of dead-letters, outside the grant and past MAIL's week. Per ADR 0376 §3-§6: the kept copy carries a per-message time to live of what is left of its stream's age (a copy already past it is kept without its body), DEAD_LETTERS and EVENTS allow per-message TTL, the list and show give no body or own headers for it, delivering it again needs a minute left and the copy keeps the time left, and its max-deliveries condition clears saying how many aged out undelivered and from which stream.
