DKIM · SPF · DMARCDomain authentication verified before production sending.
Email infrastructure for developers and AI agents
Transactional email for code and agents
Send email through API, SMTP, or AI agents.
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
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.
Features
Everything you need to send email
REST API
Send with one JSON request.
Learn moreSMTP relay
Port 587 · STARTTLS.
Learn moreDomain authentication
Set up SPF, DKIM, and DMARC.
Learn moreSigned webhooks
Delivery events with HMAC signatures.
Learn moreSuppression lists
Automatic suppression of bounces and complaints.
Learn moreDelivery logs
Search delivery statuses.
Learn moreHow it works
From API call to inbox outcome
- 01
Send
Call the REST API or submit over SMTP with a scoped project key.
- 02
Authenticate
DKIM-sign messages and validate SPF, return-path, and DMARC alignment.
- 03
Deliver
Messages queue through the pipeline with retries and reputation controls.
- 04
Observe
Webhooks and logs stream status so every send stays auditable.
Security
Built with the controls that protect deliverability
Automatic suppression
DKIM, SPF, DMARC
Signed webhooks
TLS in transit
Scoped, hashed keys
Reputation monitoring
Pricing
Start free. Scale when you are ready.
Production access is immediate on every plan. Payment changes limits, not access.
Indicative conversion. Final amount at checkout.
Sandbox
$0
- 3,000 API recipients / month
- Sending domains: 1
- API cap: 100/ day
- Mail · 1 GiB/mailbox · domains: 3
Learn more
- REST API + SMTP
- 1 sending domain
- External recipients after domain verification
- 100 emails per day
- Manual deletion
- Mail: 1 GiB per mailbox, 3 own domains
Developer
$15/mo
- 25,000 API recipients / month
- Sending domains: 5
- Mail · 1 GiB/mailbox · domains: 5
Learn more
- Everything in Sandbox
- 5sending domains
- 25,000 emails per month
- No hard daily cap
- Manual deletion
- Mail: 1 GiB per mailbox, 5 own domains
Pro
$39/mo
- 100,000 API recipients / month
- Sending domains: 25
- Mail · 1 GiB/mailbox · domains: 25
Learn more
- Everything in Developer
- 25sending domains
- 100,000 emails per month
- No hard daily cap
- Reputation monitoring
- Mail: 1 GiB per mailbox, 25 own domains
Terms & limits
Current hosted-mail capacity: 1 GiB per mailbox on every plan. API volume counts recipients, including Cc/Bcc; extra volume is blocked with 429, not billed automatically. Log records include message bodies and remain until deletion or administrator cleanup; automatic plan-based deletion is not implemented. Dedicated IP, SLA and support response times require a separate agreement. Only configured payment methods appear at checkout; YooKassa is currently enabled. Payment does not guarantee delivery or inbox placement. API monthly capacity resets at the start of each calendar month in UTC, independently of the subscription payment date.