Mailgun

Mailgun is built from the ground up as an API service for developers who send email programmatically from their applications. It provides both REST API and SMTP relay interfaces, letting teams build email directly into their software stack. The platform includes webhook support for bounce handling, spam complaints, and delivery tracking, plus validation tools for email addresses and domains.

Mailgun is ideal for SaaS companies with technical teams who want full control over email delivery and don't need a traditional marketing interface. It excels at transactional and notification emails at scale, though it requires more engineering investment than platforms targeting non-technical marketers.