As a space-saving measure, there is a task that runs periodically and from all player collections removes those messages that are
(1) marked as read (i.e., dated before the last-read-date),
(2) older than a certain expire time, and
(3) not specifically marked as "kept".
"kept" messages will show up in your @mail listing with an `=' to the right of the message number.
The first form of the @keep-mail command marks the indicated messages as kept. The message-sequence argument is as with other mail commands (see "help message-sequences"). @keep-mail without any arguments marks your current message as kept.
The second form of the command is used to remove all such marks from your mail collection.
@mail kept:
will produce a list of all messages marked as kept (see "help message-sequences").
You can use @mail-option expire (see "help @mail-option") to change your expire time.
You can use the @netforward command (see "help @netforward") to send mail to your email address for local archival.
[...At the time of this writing, player mail is taking up a large fraction of LambdaMOO's database. It would be appreciated if you not @keep any more mail than you have to...]