Email form submission issue

Hi,

New site has a contact form using the Forms App. Submissions are stored correctly, and I receive a confirmation email as well, as expected using the "Send responsive via Email" options. The issue is that the client doesn't receive any of these emails when their email address (with the same domain name as the website) is used to receive the form submissions. Any other emails addresses that aren't of the same domain name do receive the submissions.

The client has their own in-house mail server and there are no hosting accounts setup on the web site server.

Thanks!