error with an incorrect email format

Hi,

Well, that's not really true.
HikaShop does check for the validity of the email address format.
It acutally uses the function JMailHelper::isEmailAddress from the Joomla library.
And not having a dot in the domain name area of an email address is not invalid:
stackoverflow.com/questions/20573488/why...emails-without-a-dot
So Joomla tells HikaShop that the email address format is valid (which it is).
And then, HikaShop uses Joomla's email library to send the email for the order creation which apparently fails on your website because the email address is invalid based on PHPMailer's library used by Joomla's library.
So the problem is that there is an inconsistency between the check done by Joomla and the check done by PHPMailer.

The solution we're going to go with is to change the line:

			if(empty($registerData->email) || (method_exists('JMailHelper', 'isEmailAddress') && !JMailHelper::isEmailAddress($registerData->email))){

			$mailer = JFactory::getMailer();
			if(empty($registerData->email) || (method_exists('JMailHelper', 'isEmailAddress') && !JMailHelper::isEmailAddress($registerData->email)) || !$mailer->validateAddress($registerData->email)){