Client is not receiving our emails!!

[diamondhead]

Is your domains DMARC policy set to reject or accept the emails you send?

DMARC stands for “Domain-based Message Authentication, Reporting & Conformance” and is an added layer of security within your domain settings that tells email recipients what to do with your emails.  It works to make sure email recipients know that an email is coming directly from the email address owner.

They are set by default more often then usual. I don't believe its going to help OP.