Email that arrives. Insight that helps.
Send transactional email through one clean API. Test every message safely, authenticate your domains, and understand delivery from request to recipient.
One platform for every email your product depends on
Move fast without treating email like a black box.
A complete transactional email workflow.
From local development to production operations, every part of the sending lifecycle lives in one focused platform.
Purpose-built email API
Send HTML, text, attachments, templates, and custom metadata with idempotent requests and useful validation.
Explore the API →Domain authentication
Guided SPF, DKIM, and DMARC setup with scheduled health checks and verified sender identities.
Delivery intelligence
Search messages and inspect recipient-level submission, engagement, bounce, and complaint events.
Reusable templates
Create organization-owned templates and personalize content with API variables.
Sending protection
Scoped keys, IP restrictions, approval workflows, suppression lists, quotas, and reputation enforcement.
Signed webhooks
Build reliable product workflows using signed event payloads, retries, and delivery-attempt history.
Three steps. One clear path.
Build in the sandbox
Create an mp_test_ key, inspect captured messages, and simulate delivery events without contacting recipients.
Authenticate your domain
Publish the provided DNS records, verify sender identities, and request production access.
Send and observe
Switch to a live key, monitor delivery events, and connect signed webhooks to your application.
Break things safely before customers see them.
Sandbox messages pass through real validation, templates, recipient storage, usage tracking, and event history. Only outbound delivery is suppressed.
- Environment-specific credentials keep test and production traffic separate
- Rendered message previews expose content, recipients, headers, and metadata
- Event simulation tests delivered, opened, clicked, bounced, and complaint flows
mp_test_Q7f...x92Delivery suppressedA small API with serious operational depth.
Start with one endpoint and grow into templates, signed webhooks, team permissions, suppression controls, and detailed event history when you need them.
View complete API reference →curl https://nextmailer.kumulant.com/api/v1/email/send \
-H "Authorization: Bearer mp_test_..." \
-H "Idempotency-Key: welcome-1048" \
-d '{
"from": "hello@your-domain.com",
"to": ["ada@example.com"],
"template": "welcome-email",
"variables": {"name": "Ada"}
}'{"status":"sandboxed"}Start free. Grow when email becomes critical.
Plans are structured around monthly recipients. Sandbox testing is included at every level.
For integration and automated testing.
- Unlimited sandbox captures
- Event simulation
- Templates and variables
- 7-day message content
- Community support
For small products sending real email.
- 10,000 recipients / month
- 1 verified domain
- 3 team members
- Signed webhooks
- 14-day delivery logs
For growing teams with critical workflows.
- 100,000 recipients / month
- 10 verified domains
- Unlimited team members
- 30-day delivery logs
- Priority support
For high-volume and specialized delivery.
- Custom recipient volume
- Extended retention
- Dedicated sending pools
- Migration assistance
- Service-level support
Example launch pricing. Final billing and overage terms can be configured before commercial release.
“The best email infrastructure is the kind your product team can understand at a glance. Clear requests, clear events, clear ownership.”
Built for product teamsDevelopers, operators, and support working from one source of truth
Know what you are building on.
Can I test without sending real email?
Yes. Sandbox keys persist and render messages but never dispatch the outbound delivery job.
What is required for production sending?
Your organization needs platform approval, a verified domain, an active sender identity, and a live API key.
How are bounces and complaints handled?
Events update recipient history and automatically add affected addresses to the organization suppression list.
Can multiple developers share a workspace?
Yes. Invite teammates and assign owner, admin, developer, analyst, or member roles.
Are webhook payloads signed?
Yes. Every webhook includes a timestamp and HMAC signature for verification and replay protection.
Can I use templates?
Yes. Templates support reusable HTML and text content with variable substitution through the send API.
Make email infrastructure the easy part.
Build safely in the sandbox, verify your domain, and move to production with confidence.
Create your free workspace