Outbound/set create takes an uploaded message and its envelope, refuses a
sender outside the relay's domains (RL-19, RL-T10), and spools it in
spool/out/ with a queued status for each recipient. Outbound/get and
/changes report it, with push, and destroy cancels or clears one. The
inbound spool's change log is shared with it. Delivery is the next step.