An email API you can build on with confidence
Your app depends on email arriving and on knowing what happened to it. These are the guarantees the Developer API gives you.
Predictable, safe to retry
Networks fail. The API is designed so retrying never makes things worse.
- Idempotent sends
Send an Idempotency-Key and, for 24 hours, a repeated request returns the first response instead of sending twice.
How it works - Clear rate limits
Every response tells you your limit, what's left and when it resets; over the limit you get a 429 with Retry-After.
How it works - Scoped API keys
Keys are full access or sending only, and sending keys can be limited to chosen domains. Keys are shown once and stored only as a hash.
How it works
Events you can trust and won't miss
Know what happened to every email, with proof it came from us.
- Signed events
Every event is signed with HMAC-SHA256 in the Standard Webhooks format, so you can check it really came from us.
How it works - Retried for days
A failed delivery is retried on a schedule from seconds to hours. Deliveries are kept for 30 days and can be replayed.
How it works - Safe outbound calls
Webhook endpoints and attachment URLs must be public addresses, never internal networks, and executable attachments are refused.
Your sending reputation, protected
One bad list shouldn't take down your app's email.
- Account health guard
Every hour we check the last 7 days: we warn you when bounces pass 4% or complaints pass 0.08%, and pause sending at 8% and 0.16%.
How it works - Automatic suppression
Hard bounces and complaints suppress the address. Suppressed recipients are skipped, don't count toward your quota, and you get an event.
How it works - Server-side only
Calls from browsers are blocked, so an API key can't be lifted from your website's code and used by someone else.
The same care across all three products
What protects your account in the Developer API, and in the other products you use with it.
- A separate sign-in per product
Signing in or out of one product doesn't touch the others, so each one stays exactly as secure as you left it.
- Delete means delete
Deleting your account cancels every plan and permanently removes your data from all three products.
- Bot protection on our forms
Sign-up and our public forms use invisible reCAPTCHA checks and rate limits to keep automated abuse out.
- Hardened by default
Our pages are served with strict security headers, including HTTPS-only (HSTS) and protection against being framed by other sites.
- One-time codes done right
Verification codes are stored hashed, work once, and stop working after too many wrong tries.
- Docs that match the product
Our documentation describes what the product does today, checked against the code, not what we hope it will do.