Pop\Mail\Mail::setBoundary PHP Method

    public function setBoundary($bnd = null)
    {
        $this->message->setBoundary($bnd);
        return $this;
    }

 public function testSetAndGetBoundary()
 {
     $m = new Mail();
     $m->setBoundary('some-boundary');
     $this->assertEquals('some-boundary', $m->getBoundary());
 }