Resolve VPS Email Server Issues

I’m dealing with a few issues on my VPS email server managed via WHM/cPanel. The primary problem seems to be DNS misconfigurations, but I also need assistance with frozen emails and ensuring the server's security against unauthorized login attempts.

Tasks:
- Troubleshoot and fix DNS records (A, MX, SPF, DKIM, DMARC, etc.)
- Resolve frozen emails and restore normal mail flow
- Secure the server from potential threats
- Test and verify functionality of email sending/receiving

Requirements:
- Proven experience with WHM/cPanel and Exim/Dovecot
- Deep understanding of DNS configurations
- Strong troubleshooting and server security skills

I made recent changes to my DNS settings on OVH, which might have contributed to these issues.