Choosing Between API and SMTP
A Send Integration connects to your email service provider either through its API or over SMTP. Which one you use depends on the provider. This page compares the two and tells you when to pick each.
Integration Types
| Feature | API | SMTP |
|---|---|---|
| Setup complexity | Simple (API key only) | More fields (host, port, TLS, credentials) |
| Authentication | API key in header | Username/password |
| Recommended for | Most cloud ESPs | Self-hosted MTAs (PowerMTA, KumoMTA) |
| Available ESPs | SendGrid, Brevo, Postmark, Mailchimp, AWS SES, Mailgun, SparkPost, and more | SMTP.com, SMTP2GO, PowerMTA, KumoMTA, any SMTP server |
When to Use API
- Cloud-based ESP with API support
- Simpler setup and management
- Built-in authentication and error handling
When to Use SMTP
- Self-hosted mail transfer agent
- ESP only offers SMTP relay
- Need custom SMTP configuration (specific ports, TLS settings)