Why does Deskhero need DNS records on my domain?

The setup screen explains it directly: "To complete the DNS setup, please add the following records to your domain. This ensures Deskhero can securely send emails on your behalf." The records delegate email-signing keys for your domain to Deskhero, so replies your team sends from Deskhero are properly authenticated and less likely to land in spam. It is a one-time setup per domain.