How do I set the priority of a mailable?

You can set the priority of a Mailable using the priority() method.

For example:

// For a specific event
\Aero\Cart\Events\OrderConfirmation::whenSendingAsMail(function (\Aero\Events\Actions\Mailable $mailable, \Aero\Cart\Events\OrderConfirmation $event) {
    $mailable->priority(1);
});

// For all order events
\Aero\Cart\Events\AbstractOrderEvent::whenSendingAsMail(function (\Aero\Events\Actions\Mailable $mailable, \Aero\Cart\Events\AbstractOrderEvent $event) {
    $mailable->priority(1);
});

// For all events
\Aero\Events\ManagedEvent::whenSendingAsMail(function (\Aero\Events\Actions\Mailable $mailable, \Aero\Events\ManagedEvent $event) {
    $mailable->priority(1);
});

Email priority does not control how quickly it is delivered. It is a sign of importance to the recipient's email client (it may not be honoured by every provider)