The standard PHP mail function is inherently unreliable. Mailgun serves as the “Transactional API” for my email infrastructure. I do not guess if a password reset or an invoice was delivered. I use Mailgun to guarantee it.

It acts as a high-reputation relay that bypasses spam filters. For a System Thinker, the value lies in its granular logging. If a client claims they never received an order confirmation, I can trace the exact timestamp and server response code to prove delivery. It manages suppression lists and domain reputation automatically. It is a critical component for any application where communication failure is not an option.