Hi,
In the Joomla configuration, you have email settings. These defines how your website send the emails. In the "Mailer" setting, you have selected how your website (including HikaShop) sends the emails:
i.imgur.com/cmsQN6l.png
If you select "sendmail" or "PHP mail", which is the case in 99% of the cases, the emails sent by your website (all of them, including all the ones sent by HikaShop, and including the ones sent to gmail) go through your hosting mail server. And it's your hosting mail server which then sends them to the recipient email server ( which can be gmail, hotmail, etc). I'm not telling you to contact the recipient email server ( gmail ). I'm telling you to contact the sender email server ( the hosting provider ).
Both Gmail and the hosting provider email servers have logs about the emails being sent and received, but you'll more likely get an answer from your hosting, since you're paying them for that service (which is included with the hosting of the website).