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Transactional email API · live on Free

The transactional email API with flat pricing and zero per-email markup.

Send transactional email at scale without the per-message bill or the deliverability headache. Senddio runs a carefully warmed mail engine, verifies your SPF, DKIM and DMARC records inside the dashboard, and uses the same simple /v1/send endpoint as your SMS, WhatsApp and Slack messages.

Start free See API reference
● Free forever · No card · All 6 channels · AI credits
POST /v1/send · channel: email
200 OK · 38ms
curl https://api.senddio.com/v1/send \
  -H "Authorization: Bearer sdo_live_…" \
  -H "Content-Type: application/json" \
  -d '{
    "channel": "email",
    "from":    "hello@yourdomain.com",
    "to":      "dev@example.com",
    "subject": "Welcome to Senddio",
    "html":    "<p>Your first send is free.</p>",
    "tags":    { "type": "welcome", "tier": "free" }
  }'

# → { "id": "sdo_msg_2K9xQ7w", "status": "queued" } in <50ms
Channel
Email
Postal 3 on Hetzner
Free plan
300/day
sampler limit
Same endpoint
/v1/send
POST · Bearer auth
Latency
<50ms
queue accept · p99
How it works

Email, in four short steps.

We do the boring, anxious parts of email — the parts that used to keep you up — so you don't have to think about them ever again.

01
Step 01
You tell us your domain.
We generate the records that make you look trustworthy to every inbox on Earth. No more copy-pasting DNS strings at midnight.
02
Step 02
You write the email.
HTML, plain text, attachments, a single subject line — your call. One POST sends it.
03
Step 03
We send it the right way.
From IPs we've spent years warming, with retries, bounce handling and reputation work running quietly in the background.
04
Step 04
You see what happened.
Opens, clicks and bounces in one feed. If something goes wrong, we tell you before your customers do.

One endpoint, one key, one bill. That is all.

The shift

Stop dreading the email bill every month.

  • No more per-thousand surprises on the invoice.
  • No more wrestling with DNS records on a Friday night.
  • No more bounce reports nobody on the team reads.
  • No more weekends spent fixing email delivery.

You get to focus on building your product.

Beyond the obvious

Whatever your team can imagine, this endpoint will send.

Real teams ship email on Senddio for everything from order receipts to late-night customer apologies. Here are a few of the things they have built — and the kinds of things your team will dream up next month.

Invoice receipts the day they were promisedMagic-link sign-in for the second deviceBeta invites that feel handwrittenAbandoned-cart nudge, with the dog photoLicense-key delivery five seconds after StripeWeekly digest that condenses 47 eventsApology email an agent wrote at 3amGDPR data export, signed link, expires SundayNPS survey only to users who logged in twiceRefund confirmation with the math shownRenewal reminder six weeks before card expiryInvoice receipts the day they were promisedMagic-link sign-in for the second deviceBeta invites that feel handwrittenAbandoned-cart nudge, with the dog photoLicense-key delivery five seconds after StripeWeekly digest that condenses 47 eventsApology email an agent wrote at 3amGDPR data export, signed link, expires SundayNPS survey only to users who logged in twiceRefund confirmation with the math shownRenewal reminder six weeks before card expiry
Contract sign-back, e-signed in two clicksCustomer-birthday note with their couponError report to admins with the trace inlineAgent-curated changelog from yesterday's PRsPostmortem to subscribers within the hourAI lead-nurture sequence, branched on behaviorCalendar invite, with the right time-zoneEducational drip for the week-2 graduatesRe-engagement email when the streak breaksQuote of the day from your knowledge baseFounder note when MRR crosses a milestoneContract sign-back, e-signed in two clicksCustomer-birthday note with their couponError report to admins with the trace inlineAgent-curated changelog from yesterday's PRsPostmortem to subscribers within the hourAI lead-nurture sequence, branched on behaviorCalendar invite, with the right time-zoneEducational drip for the week-2 graduatesRe-engagement email when the streak breaksQuote of the day from your knowledge baseFounder note when MRR crosses a milestone
The thing you'll build next month
If you can describe it in one sentence, you can ship it on /v1/send.
Read the docs
What you get

Production-ready email, on day one.

The boring infrastructure — signing, retries, suppressions, webhook verification, audit — is done. Your code is one POST.

  • Postal 3 mail engine on Hetzner-owned IPs
  • SPF / DKIM / DMARC verification in-app
  • Bounce classification: SMTP 5xx → suppress, 4xx → retry 3× exp.
  • Open + click tracking with one-pixel + signed redirects
  • Spam complaint feedback loop ingestion
  • Disposable-email protection on Free + Starter
  • Reputation monitoring + auto-pause on anomaly
  • Threaded inbound replies via Postal webhook
From teams who switched

You're in good company on Email.

Composite quotes from interviews with current Senddio customers shipping email in production.

We moved 2.1 million monthly emails in a single afternoon. The bill dropped by 67%, bounces fell to under half a percent, and the dashboard actually tells you what is wrong with your DNS. We had never seen that before.
Léo M.
Backend lead · fintech, 40 engineers
Email authentication finally made sense because the verification page showed me exactly what was wrong. It sounds small, but it gave me a Saturday back.
Priya R.
Founder · solo SaaS
Our Claude agent writes its own customer receipts and labels them with its name. Spend per agent is right there as a line item, and our finance team has never been calmer.
Aaron T.
Founder · workflow tool
Compared to your alternatives

Senddio vs. email-only vendors

FeatureSenddioDoing it yourself
Channels in one API61 (email only)
AI agent connectorsClaude MCP + OpenAI—
Per-email markup$0Yes, scales w/ volume
Free plan300/day · all channels100/day · email only
Dedicated IPsEnterpriseAdd-on, $$$
Source-available mail enginePostal 3 (open core)Black-box
Your next 30 days

What changes once you ship Email on Senddio.

01
Day 1
First email shipped from your verified domain
02
Day 3
SPF / DKIM / DMARC green across every record
03
Week 1
Bounce rate under 0.5%, complaints negligible
04
Day 30
Sending below the price of one team lunch
●Every milestone above ships on the Free plan. No card, no upgrade gate.
RelatedSPF— Sender Policy Framework — prevents spoofingDKIM— DomainKeys Identified Mail — email signingDMARC— Policy that governs SPF + DKIM failures
FAQ

Email — FAQ

SendGrid, Postmark and Resend send email only. Senddio sends email, SMS, WhatsApp, push notifications, Slack and Telegram through one endpoint and one bill. Senddio uses flat monthly pricing with no per-email markup, and ships first-class connectors for Claude and ChatGPT agents. SendGrid and Postmark charge per-thousand emails on top of plan fees; Resend has comparable developer experience for email alone but does not cover the other channels.

The free plan includes 300 emails per day (around 9,000 a month), one verified sending domain, one API key, and seven days of log history. You also get sampler limits on every other channel and 20 AI credits a month to try features like spam scoring and template generation. No credit card needed.

Senddio generates the exact DNS records you need for SPF, DKIM and DMARC. You add them to your DNS provider once, and the Domains page polls every minute to confirm they are in place. If a record is wrong, Senddio shows you the difference between what is expected and what is published so you can fix it in seconds.

Hard bounces (permanent failures) are automatically added to your suppression list and never retried, protecting your sender reputation. Soft bounces (temporary failures) are retried three times with backoff before being suppressed. You can see and export every suppression from the dashboard.

Yes. Inbound replies arrive on a webhook, are threaded under the original message in your Logs, and can be forwarded to Slack or Telegram for human or AI-agent triage.

Other channels
SMS
Programmable SMS API
WhatsApp
WhatsApp Business API
Push
Push notification API
Slack
Slack messaging API
Telegram
Telegram bot messaging

Ship email in 5 minutes.

Free forever — on the same plan as all 5 other channels, plus AI credits.

Start free See pricing
● 300 emails/day · All 6 channels · AI credits · No card