From email address not same as domain

I have many sites where the domain used for my clients emails is different to the domain of the website install. When entering this as the ‘From’ email in CF7 setup there are warnings that the setup is wrong. I have other sites that use Gravity Forms, and the same setup is not an issue.
If I use a fake ‘From’ email on the actual domain such as no-reply@…..
The notification is not sent, and on tracing emails there is a notice that it was quarantined due to no valid MX Record, so I have to use a valid email, but not an email of the same domain as the website. How do I avoid the error/warning notice in the cf7 form settings?