Sets the priority of this message.
The value is an integer where 1 is the highest priority and 5 is the lowest.
$this
public function priority(int $priority) : static { if ($priority > 5) { $priority = 5; } elseif ($priority < 1) { $priority = 1; } return $this->setHeaderBody('Text', 'X-Priority', \sprintf('%d (%s)', $priority, self::PRIORITY_MAP[$priority])); }