Mailgun DNS Configuration Expert

I need help configuring DNS settings for sending marketing emails through Mailgun. This setup needs to work with Apollo.io integration.

Requirements include:
- Setting up SPF, DKIM, and DMARC records
- Configuring DNS for an existing domain

Ideal skills and experience:
- Expertise in DNS management
- Experience with Mailgun and email authentication protocols
- Familiarity with Apollo.io integration

Please provide examples of similar work done.