Engineering··Nixify Team
SMTP vs API-based Email Verification
Understanding the tradeoffs between SMTP-based OTP delivery and API-based verification services.
SMTP vs API-based Email Verification
When building an email verification system, you have two main options: SMTP-based delivery or API-based services.
SMTP-based delivery
SMTP delivery sends the email directly from your server. This gives you full control over the transport layer.
Pros:
- Full control over the email pipeline
- No third-party API dependency
- SMTP transport is operator-configurable (relay or managed service)
- Lower cost at scale
Cons:
- Requires managing email deliverability
- IP reputation is your responsibility
API-based services
Services like SendGrid, Resend, or Postmark handle delivery via their API.
Pros:
- Managed deliverability
- Built-in analytics and webhooks
- Less infrastructure to maintain
Cons:
- Vendor lock-in
- Per-email pricing
- Less control over the transport
Nixify's approach
Nixify's hosted API exposes a clean OTP send/verify contract to customers — hosted API customers do not provide SMTP credentials. The operator-side mail transport is configured by the platform operator and is separate from the customer-facing API contract.