MessageUserType::onBeforeSaveAll

static function onBeforeSaveAll($userField, $mailIds, $userId)
{
	$previousMailsIds = (array) $userField['VALUE'];
	if ($previousMailsIds !== false)
	{
		$result = static::deleteList([
			'!@MESSAGE_ID' => $mailIds,
			'=ENTITY_UF_ID' => $userField['ID'],
			'=ENTITY_TYPE' => $userField['ENTITY_ID'],
			'=ENTITY_ID' => $userField['VALUE_ID'],
		]);
	}
	$newMailIdsToSave = array_diff($mailIds, $previousMailsIds);
	foreach ($newMailIdsToSave as $mailMessageId)
	{
		static::onBeforeSave($userField, $mailMessageId, $userId);
	}
}