MessageAccess::getEntitiesForType

public function getEntitiesForType($entityType): array
{
	$collection = $this->getCollection($this->getMessage());

	$bindings = [];

	/** @var BitrixMailItemMessageAccess $item */
	foreach ($collection as $item)
	{
		if ($item->getEntityType() === $entityType)
		{
			$bindings[] = $item->getEntityId();
		}
	}

	return $bindings;
}