Email not being received

http://www.hiddendepthshypnotherapy.com/index.php/about-me

Completing the Contact form on this site appears to send the email but nothing is being received. It was originally set up using PHP mail, but I have now changed it to SMTP, but neither method seems to be working. Can you offer any suggestions on this?

Thanks for your help.

Regards,

Gary

Thanks for the quick reply Christopher. I have checked and caching is disabled so it can't be that. Which URL did you? want to see to check it?

Christopher,

Thanks for your response. Further testing has revealed that the contact message is being sent and received correctly. However it is when a copy is requested to be sent to the person sending the message that this is not being delivered. It is eventually returned as undeliverable with the following error details:

"This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

mavrosxristoforos@gmail.com
host gmail-smtp-in.l.google.com [108.177.15.26]
SMTP error from remote mail server after end of data:
550-5.7.26 Unauthenticated email from ymail.com is not accepted due to domain's
550-5.7.26 DMARC policy. Please contact the administrator of ymail.com domain
550-5.7.26 if this was a legitimate mail. Please visit
550-5.7.26 https://support.google.com/mail/answer/2451690 to learn about the
550 5.7.26 DMARC initiative. s8si26456072wri.520 - gsmtp"

I have been to the link in this email but cannot really understand what it is saying, although it does appear to be unique to GMail. I have tried a couple of things but it doesn't make any difference the copy email is not being delivered. Have you come across this before and do you know what to do about it?

Thanks for your help.

Regards,

Gary