Email infrastructure for developers and AI agents

Transactional email for code and agents

One delivery platform across REST, SMTP, the official Node SDK, and MCP — with durable queues, signed webhooks, templates, and real delivery outcomes.

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LIVE
curl https://api.srs-postline.com/v1/emails \  -H "Authorization: Bearer srs_live_..." \  -H "Idempotency-Key: reset-4821" \  -d '{    "from": "noreply@yourapp.com",    "to": "user@example.com",    "subject": "Reset your password"  }'

Built for modern sending stacks

DKIM · SPF · DMARCDomain authentication verified before production sending.
HMAC-signed webhooksEvery event signed with HMAC-SHA256, SSRF-resistant delivery.
TLS in transitSupported network hops are encrypted end to end.
Status pageCurrent scope and operational notices, no invented SLA.

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Features

Everything you need to send email

A focused stack for transactional delivery — API, SMTP, authentication, and observability.

REST API

Send with one JSON request. Idempotency keys prevent duplicate deliveries.

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SMTP relay

Drop-in SMTP on port 587 with STARTTLS for any language or mail client.

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Domain authentication

Guided DKIM, SPF, and DMARC setup before production sending is enabled.

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Signed webhooks

Delivery, bounce, and complaint events signed with HMAC-SHA256.

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Suppression lists

Hard bounces and complaints are suppressed automatically with manual overrides.

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Delivery logs

Searchable metadata from queue to recipient-server accept or failure.

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How it works

From API call to inbox outcome

Connect your app, authenticate the domain, send, and watch every event.

  1. 01

    Send

    Call the REST API or submit over SMTP with a scoped project key.

  2. 02

    Authenticate

    DKIM-sign messages and validate SPF, return-path, and DMARC alignment.

  3. 03

    Deliver

    Messages queue through the pipeline with retries and reputation controls.

  4. 04

    Observe

    Webhooks and logs stream status so every send stays auditable.

Security

Built with the controls that protect deliverability

Implemented controls, not aspirational claims — see the full security page for details and current limitations.

Automatic suppression

Hard bounces and complaints are suppressed project-wide before the next send.

DKIM, SPF, DMARC

Guided domain verification with DNS checks before production access.

Signed webhooks

HMAC-SHA256 signatures, bounded retries, SSRF-resistant outbound delivery.

TLS in transit

Encrypted network hops for API, SMTP, and webhook delivery.

Scoped, hashed keys

Test and live API keys are separate, scoped, and never stored in plaintext.

Reputation monitoring

Abuse and reputation signals are monitored across the sending pipeline.

Read the security page →

Pricing

Start free. Scale when you are ready.

Production access is immediate on every plan. Payment changes limits, not access.

Converted at today's exchange rate for reference — your account may be billed in a different currency at checkout.

Sandbox

$0

Build and test with verified recipients.

  • REST API + SMTP
  • 1 sending domain
  • Verified recipients only
  • 100 emails per day
  • 7-day metadata logs
Get started

Developer

$15/mo

For approved early-stage products.

  • Everything in Sandbox
  • 5sending domains
  • 25,000 emails per month
  • No hard daily cap
  • 30-day metadata logs
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Pro

$39/mo

For approved production workloads.

  • Everything in Developer
  • 25sending domains
  • 100,000 emails per month
  • No hard daily cap
  • Reputation monitoring
Get started

See full pricing →

FAQ

Frequently asked questions

Need higher volume or a custom setup? We are happy to help.

Create an account and a production API key. Test to your own email before domain verification, then send to any recipient.

Contact us →