Hey there,
After reviewing your project description its clear that you have some problem in your email delivery from your WHM cPanel.
I'm very experienced with System Administration, Network Administration, SMTP Server Configuration and Troubleshooting, SMTP Authentication(SPF, Dkim, Dmarc, rDNS), SMTP IP/Domain Reputation.
I'll be happy to fix this issue for you.
Thanks in advance for giving the opportunity to working with you.
Have a good day.
Best Regards,
Serazum Munir.