customer not getting emails

-- url of the page with the problem -- : www.dannyabrahamsart.com/
-- HikaShop version -- : 4.2.2
-- Joomla version -- : 3.9.11

Hi,

I have a new problem. It looks like customer do not get a confirmation after placing an order. I do get a return message with subject Mail delivery failed: returning message to sender.

It looks like gmail has made some changes recently and is refusing an email from hikashop?

sarah********@gmail.com
host gmail-smtp-in.l.google.com [209.85.232.27]
SMTP error from remote mail server after end of data:
550-5.7.1 Unauthenticated email from yahoo.com is not accepted due to domain's
550-5.7.1 DMARC policy. Please contact the administrator of yahoo.com domain if
550-5.7.1 this was a legitimate mail. Please visit
550-5.7.1 support.google.com/mail/answer/2451690 to learn about the
550 5.7.1 DMARC initiative. d23si1757194qto.11 - gsmtp

Please advice how to solve this problem.

Hi,

The log you provided indicates that your domain name is not properly configured to send emails with DMARC support:
www.sparkpost.com/resources/email-explained/dmarc-explained/
So it's not really a HikaShop problem, evne though it affects the emails sent by HikaShop since they use your domain name.
So you need to properly setup DMARC with your domain name and the emails (sent by HikaShop or other extensions/Joomla) won't be flagged as spam because a lack of it.