What is transactional email?

Transactional email is a message sent to one recipient in response to something they did: a password reset, a receipt, an email verification, or a security alert. Unlike marketing email it is expected, time-sensitive, and usually blocking, so a silent failure stops the user from finishing what they started.

Is Apollo Signal free to start?

Yes. The Spark plan includes 3,000 emails per month, the REST API, the SMTP relay, signed webhooks, open and click tracking, and SPF, DKIM, and DMARC setup without a credit card.

Should I use the REST API or the SMTP relay?

Both run on the same delivery infrastructure, domains, and event pipeline, so the choice is about integration effort. Use the SMTP relay on port 587 with STARTTLS when you already have a working mailer, and the REST API or a typed SDK when you want typed requests and per-message control.

What happens after the API accepts an email?

Accepted, delivered, opened, clicked, bounced, and complained events are delivered to your configured endpoints as HMAC-signed webhooks with automatic retries, so your application can react to the outcome instead of assuming the send worked.

How does Apollo Signal protect email deliverability?

Signal guides SPF, DKIM, and DMARC setup, then keeps checking domain health after launch. Automatic suppressions and complaint tracking stop repeat sends to addresses that already bounced or complained, which is what protects your sending reputation over time.

Can I migrate from Resend, SendGrid, Mailgun, or Postmark?

Yes. Guided migrations move domains, suppressions, contacts, segments, templates, and message history from Resend, SendGrid, Mailgun, Postmark, and Brevo, limited to what each source provider exposes. You can verify domains and test events before redirecting production traffic.

Can I send from my own AWS account?

Yes, on the Enterprise plan. Bring Your Own Cloud routes sending through your own AWS account using a sending-only scoped grant, so Apollo stores no access keys or passwords, and delivery automatically falls back to Apollo infrastructure if the connection is removed.

Apollo Signal3,000 emails every month, free

Send the email. Know where it lands.

Password resets, receipts, and alerts your users actually receive. One call sends the message, then signed events tell you whether it was delivered, opened, or bounced. Start free with 3,000 emails a month—no card required.

Read the documentation

Transactional email fails quietly. A 202 response is not a delivery.

Know before your users tell you: When a password reset bounces, the user cannot get in—and you find out from a support ticket instead of your own system. Signal reports accepted, delivered, opened, clicked, bounced, and complained as one signed event model your application can act on.
One searchable delivery history: Follow a single message from the request your app made, through domain configuration and provider handoff, to the final recipient event. No stitching log sources together while an incident is open.

Integrate once. Follow every message.
Improve the next send.

Integrate

Start with the interface your application already uses. Send through the API, an SDK, or SMTP with one project key.

REST API and typed SDKs
SMTP relay on port 587
Scoped test and live keys

apollo-signal — init

Detecting runtime... node 22 (typescript)

added @apollo-signal/node@1.4.2

created signal.config.ts

Linked project key sk_live_****4f2a

scopes: emails:send, events:read

Verifying REST transport... 202 Accepted

Verifying smtp.apollosignal.com:587... STARTTLS ok

Registered webhook https://acme.com/hooks/signal

signing secret whsec_****91c3 stored

Sandbox probe queued... signature verified

integration ready · rest + smtp + webhooks

LINKINGacme/web

Test

Exercise the complete flow without touching an inbox. Sandbox sends return realistic API responses and webhook events while protecting real recipients.

Bounce and complaint simulation
Webhook signature testing
Separate test and live traffic

Observe

Stream delivery state back into your product. HMAC-signed webhooks make message state useful in support, billing, authentication, and analytics workflows.

HMAC-signed payloads
Automatic delivery retries
Real-time event stream

Protect

Keep reputation work in the sending loop. Guided authentication, suppression handling, and domain health checks surface issues before inbox providers do.

SPF, DKIM, and DMARC checks
Automatic suppressions
Reputation monitoring

The tools around the send matter.
They should arrive together.

Risk-free sandbox. Validate requests, events, and failure handling before real recipients enter the loop.

Signed webhooks. Verify every event on arrival and let retries handle temporary endpoint failures.

Useful engagement. Read opens, clicks, and unsubscribes by template and over time without exporting raw events.

One delivery layer. Whatever your stack.

Use the typed client that fits your service, call the REST API directly, or keep the mailer you already run. Whichever path you pick, you get the same verified domains, the same events, and the same plan limits.

Explore integration guides

One project and event model across every integration path—including the SMTP relay.

TypeScript

Typed requests for Node.js and web frameworks.

Python

Straightforward sending for workers and APIs.

Go

A small client for high-throughput services.

Kotlin

Typed sending for JVM services and Kotlin apps.

Switching providers should not mean starting over.

Guided migrations bring domains, suppressions, contacts, templates, and message history across from Resend, SendGrid, Mailgun, Postmark, and Brevo—as far as each provider exposes them. Verify the new path first, then move production traffic. Still deciding? Compare Signal against other providers.

Guided imports. See what each provider can move before the migration begins.

Controlled cutover. Verify domains and test events before redirecting live sends.

Open the migration assistant

Resend
SendGrid
Mailgun
Postmark
Brevo

Pricing that follows sending volume, not feature gates.

Start free at 3,000 emails a month. Ignite covers 50,000 for $15, and every tier keeps the same API, SMTP relay, signed webhooks, and deliverability tooling—you are paying for volume, not unlocking features.

Billed monthly, so there is no annual contract to commit to. See how this compares with other providers.

Spark

Ship the first transactional email without a card.

Free

no card required

3,000 emails / month
100 sends / day
1 project · 1 domain
REST API and SMTP
Signed webhooks
Open and click tracking
SPF, DKIM, DMARC
30-day retention

Ignite

Steady transactional volume, no daily cap.

$15

then $0.50 / 1k

Everything in Spark, plus:
50,000 emails / month
No daily send limit
5 projects · 10 domains
Custom tracking domain
Read engagement
Deliverability advisor
Real-time event stream
90-day retention

Growth

Room to grow across more products and domains.

$35

then $0.42 / 1k

Everything in Ignite, plus:
150,000 emails / month
10 projects · 25 domains
25 API keys
50 AI credits / month
Send time optimisation

Pulse

Higher volume with regional delivery.

$65

then $0.36 / 1k

Everything in Growth, plus:
300,000 emails / month
25 projects · 100 domains
Multi-region sending
100 AI credits / month

Scale

Millions of messages with longer history.

$180

then $0.30 / 1k

Everything in Pulse, plus:
1,000,000 emails / month
100 projects · 250 domains
250 AI credits / month
180-day retention

Pay as you go

No monthly commitment. $0.40 per 1,000 emails.

No daily send limit
5 projects, 10 domains, 10 webhooks
REST API and SMTP relay
Custom tracking domain
Read engagement and scroll depth
Deliverability advisor
Real-time event stream
20 AI credits per month
90-day log retention

Enterprise

Custom pricing for committed volume and compliance requirements.

Unlimited emails, projects, and domains
Dedicated IPs included
Multi-region sending
SAML single sign-on
Unlimited AI credits
365-day log retention
Priority support
Uptime SLA and custom contract

Questions before the first send

What teams ask when they are choosing a transactional email provider.

Can't find what you're looking for? Contact our support team

Apollo Signal