What are transactional ESPs (e.g., Postmark, SparkPost, Mailgun)?

Transactional ESPs specialize in triggered, one-to-one messages: password resets, order confirmations, shipping notifications, and account alerts. They prioritize delivery speed, reliability, and developer-friendly APIs over marketing features.

Key characteristics: fast delivery (often seconds), high deliverability (sending expected messages helps), simple APIs for integration, robust logging and debugging, and minimal marketing features. Postmark is famous for delivery speed; Mailgun emphasizes developer experience.

Many organizations use transactional ESPs alongside marketing platforms. Transactional messages need different treatment: higher urgency, cleaner reputation (recipients expect them), and technical integration rather than campaign management. Separating streams protects both.