code: public function activateAccount($objUser)
  	{
  		$arrNewsletters = StringUtil::deserialize($objUser->newsletter, true);
  
  		// Return if there are no newsletters
  		if (!\is_array($arrNewsletters))
  		{
  			return;
  		}
  
  		// Activate e-mail addresses
  		foreach ($arrNewsletters as $intNewsletter)
  		{
  			$intNewsletter = (int) $intNewsletter;
  
  			if ($intNewsletter < 1)
  			{
  				continue;
  			}
  
  			$this->Database->prepare("UPDATE tl_newsletter_recipients SET active='1' WHERE pid=? AND email=?")
  						   ->execute($intNewsletter, $objUser->email);
  		}
  	}
docs: Activate newsletter subscription of new users
  
  @param MemberModel $objUser