I have a client whose email is hosted on her web host. She has set her Gmail account to download all the email from her web host, and reply using whatever the domain name is in the To field.
I have the DMARC on my own domain set to reject because of the quantity of spam I receive.
All email to me ,sent from her Gmail account, is rejected. I'm assuming it's because her domain name and the source of the Gmail reply are not in sync.
Is there a way that both of us can keep our setup, but that I can receive her replies to my email to her branded address?
If you send an email from Nora@yourdomain.com to Client@WebhostDomain.com and your client follows the steps in this article, she may be using Gmail's interface, but the email is being relayed by the SMTP host configured in Step 1, bullet #7.
If your client didn't add an SPF record to her domains that lists that SMTP server (step 1, bullet #7) as authorized sending server (or add DKIM signing for her domain), then the email might be considered as spoofed email.
The error message your client is receiving may (or may not) support this analysis.