DMARC issue

I have been having an issue with TripAdvisor emails and Help Center form submissions, which started about a month ago. I suspect it's part of this DMARC issues being reported, but I cannot figure out anything beyond that. 

I am just a TripAdvisor member/user, but the mail rejection script looks like this: 

This is what the mail failure notice looks like. 

Mail delivery failed: returning message to sender
 
Mail Delivery System<mailer-daemon@ndh-exim-01>

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:

  sfwebform@tripadvisor.com
    host smtp.google.com [74.125.24.27]
    SMTP error from remote mail server after pipelined end of data:
    550-5.7.26 Unauthenticated email from comcast.net is not accepted due to
    550-5.7.26 domain's DMARC policy. Please contact the administrator of
    550-5.7.26 comcast.net domain if this was a legitimate mail. To learn about the
    550-5.7.26 DMARC initiative, go to
    550 5.7.26  https://support.google.com/mail/?p=DmarcRejection d9443c01a7336-2365d8ad0f1si193846695ad.127 - gsmtp

This is what the delivery-status.txt looks like: 

Reporting-MTA: dns; ndh-exim-01

Action: failed

Final-Recipient: rfc822;sfwebform@tripadvisor.com

Status: 5.0.0

Remote-MTA: dns; smtp.google.com

Diagnostic-Code: smtp; 550-5.7.26 Unauthenticated email from comcast.net is not accepted due to domain's DMARC policy. Please contact the administrator of comcast.net domain if this was a legitimate mail. To learn about the DMARC initiative, go to https://support.google.com/mail/?p=DmarcRejection d9443c01a7336-2365d8ad0f1si193846695ad.127 - gsmtp

It would seem that TA reps are not getting my submissions, they seem to disappear and are not being sent. 

I have never changed a single setting on my comcast email account for years, and I access it from my firefox web browser on my PC and also Safari web browser on my iPad. 

Thank you for any insight and help you can offer. I am not any kind of IT person.

Brad