Email service providers
Compare managed sending and inbound services, understand what an ESP operates, and choose the integration your application needs.
Reviewed
An email service provider (ESP) operates email infrastructure for your application. Many offer an HTTP sending API and SMTP submission; some also accept inbound messages and deliver them to your application. Do not assume a sending provider offers mailbox storage or an inbound webhook.
Match the service to the workflow
| Workflow | Verify before choosing |
|---|---|
| Transactional messages | SDK support, authenticated domains, bounce events, retry/idempotency behavior, and account limits |
| Incoming application mail | MX or forwarding setup, payload format, signature verification, attachments, and event retries |
| Newsletters | Consent, unsubscribe/suppression handling, broadcast separation, and acceptable-use rules |
| Human mailboxes | Whether mailbox access, storage, and client protocols are actually included |
Resend’s introduction separates transactional messages and marketing broadcasts and leads with domain verification and an API key. Postmark’s developer documentation separately documents sending, inbound processing, message streams, and webhooks. These are examples of capabilities to check, not a claim that all providers share those features or policies.
What the provider handles—and what you retain
Managed infrastructure removes host provisioning, queue-server maintenance, and some reputation operations. Your application still owns recipient permissions, content quality, secret handling, event processing, suppression behavior, and sensible retry decisions.
Before migration, compare how the current and new providers identify messages, signal acceptance versus delivery, retry webhooks, represent attachments, and authenticate callbacks. A successful send API response is not proof of final delivery.
Find an integration walkthrough
The main guide contains provider-specific sending guides and inbound parsing guides. Those links open the main guide and its own menu. This server guide remains the place for infrastructure concepts and server/provider integration documentation as it is published.
MailKite combines inbound webhooks and an outbound API for application workflows. Follow its quickstart, sending reference, and webhook verification documentation for the supported implementation path. Future server-specific SDKs are not a prerequisite or an available download in this guide today.