List Flag: deferred

When handling submissions, listmanager normally instructs the mail system
to attempt delivery right away in the background.  If this flag is set,
listmanager will instruct the mail system to attempt delivery during its
next run through the mail queue rather than beginning to do deliveries
right away.  This reduces load on the machine where listmanager operates,
and listmanager runs notably faster when handling submissions because the
mail system returns immediately, but the distribution of submissions takes a
while longer.

This flag can only be set or cleared by system administrators through the
listmanager command line interface.