Mailgun API + Your Own Email Server (FastPanel): a Practical Setup That Passes Gmail (SPF/DKIM/DMARC)
A practical, human-readable guide to combine Mailgun API for transactional sending with a FastPanel mail server for real mailboxes and inbound delivery. Includes DNS (MX/SPF/DKIM/DMARC), PTR, testing, and the exact fix for Gmail 550 5.7.26 unauthenticated sender.