How do crypto payments work?

Credits are strictly pay-as-you-go at $5 per 1,000 emails ($0.005 per send). You can top up balances on-chain using Bitcoin (BTC), Ethereum (ETH), Solana (SOL), USDT, or USDC. Balances never expire.

Why did my request return HTTP 422?

SkyRelayer runs pre-flight spam scans via SpamAssassin and Rspamd. If your content triggers spam or phishing flags, delivery halts with an HTTP 422 status and score diagnostics so your domain reputation stays protected.

How does display name anti-phishing validation work?

Sender display names cannot simulate domain names, IP addresses, or include characters like @, , or quotes. Lookalike unicode characters are automatically sanitized.

Can I audit message delivery steps in real time?

Yes. Every message generates an audit log recording millisecond timings for queuing, anti-spam screening scores, MTA handoff latency, and recipient open events.

Transactional email without subscriptions.

Q: How do the 15 free API credits work?

Every newly created account automatically receives 15 complimentary API credits. You can immediately generate live API keys, enroll custom domains, and send test or production emails without adding cryptocurrency.

Q: How does the POST /v1/send endpoint authenticate?

Requests authenticate via a Bearer token header (Authorization: Bearer sk_live_...). API keys can be generated, labeled, and revoked instantly inside the dashboard.

Q: What are the payload and file attachment limits?

POST /v1/send accepts application/json or multipart/form-data. Maximum HTML size is 2MB, plain text is 1MB, up to 50 recipients per request, and up to 10 attachments totaling 25MB. Executables (.exe, .bat, .cmd, .js) are strictly rejected.

Q: Does open tracking break DKIM cryptographic signatures?

No. The 1x1 zero-opacity tracking pixel is injected into the HTML prior to RFC 822 MIME compilation and 2048-bit RSA DKIM signing, guaranteeing valid inbox body hashes.

High-deliverability Postfix SMTP relay dispatch. Pay just $5 per 1,000 emails using crypto. No monthly minimums, no expiring balances, and zero spam surprises.

Start with 15 Free Credits Estimate Costs

$0.005

Per Send

< 90ms

API Latency

2048-bit

Auto DKIM

100%

Pay-As-You-Go

curl -X POST https://api.skyrelayer.com/v1/send \
  -H "Authorization: Bearer sk_live_..." \
  -H "Content-Type: application/json" \
  -d '{
    "from": "\"Auth Desk\" <hello@yourcompany.com>",
    "to": "user@domain.com",
    "subject": "Your security code",
    "html": "<p>Passcode: <strong>382-910</strong></p>"
  }'

# Returns 200 OK & consumes 1 credit:
# { "success": true, "messageId": "<SR-91823>", "durationMs": 84 }

Architected for strict inbox deliverability

Everything you need for clean sender reputation, zero proxy warnings, and rapid API execution.

Automated DKIM & SPF

2048-bit RSA keys generated instantly upon domain enrollment. Direct return-path CNAME entries eliminate third-party proxy flags.

Pre-Flight Spam Defense

Dual pre-flight checks via SpamAssassin and Rspamd block suspicious payloads before SMTP handoff, preventing domain blacklisting.

Live Delivery Timelines

Audit every dispatch step-by-step: API ingestion, spam screening scores, Postfix MTA handoff, and recipient read notifications.

How SkyRelayer compares

Designed for developers who despise monthly plan traps, credit expiry, and sudden overage charges.

Feature	SkyRelayer	SendGrid / Mailgun	AWS SES
Payment Model	Pay-as-you-go ($5 / 1k)	Monthly subscription tiers	Metered utility bill
Credit Expiration	Never expire	Reset monthly (lost if unused)	N/A
Payment Options	Crypto (BTC, ETH, SOL, Stablecoins)	Credit Card only	AWS Account Card
Spam Pre-Scan	Included (SpamAssassin + Rspamd)	Post-delivery bounce reports	No pre-flight inspection
Initial Credits	15 free on signup	Requires card verification	Sandboxed environment

Transparent Crypto Pricing

No tiers, no contracts. Top up whenever you need.

$25 USD

$0.005 / email

Volume Needed 5,000 emails

Instant on-chain confirmation · Balance never expires

BTC ETH SOL USDT USDC

Claim 15 Free Credits & Generate Key

Frequently Asked Questions

Technical specifications, security safeguards, and payment details.

How do the 15 free API credits work?

Every newly created account automatically receives 15 free API credits. You can immediately generate live API keys (sk_live_...), enroll your domains, and send 15 live or test messages without depositing crypto.

How do crypto deposits work?

Credits are strictly pay-as-you-go at $5 per 1,000 emails ($0.005/email). You can top up your balance whenever needed via BTC, ETH, USDT, USDC, or SOL. Deposited balances never expire, and there are no recurring subscription fees.

How does the POST /v1/send endpoint authenticate?

Calls to /v1/send require a standard Bearer token header: Authorization: Bearer sk_live_.... You can generate custom-named keys and revoke compromised keys instantly via the API Keys console in your dashboard.

What are the payload and file attachment limits?

The endpoint accepts application/json or streamed multipart/form-data. Limits include: max 2MB for HTML body, 1MB for plain text, max 50 recipients per call, and up to 10 attachments totaling 25MB. Dangerous executable extensions (such as .exe, .bat, .cmd, .iso) are rejected immediately.

Why would a request return HTTP 422?

Before any email reaches the MTA, it undergoes pre-flight screening via SpamAssassin and Rspamd. If your payload triggers severe spam or phishing rules, the request returns HTTP 422 SPAM_DETECTED along with diagnostic score breakdowns. This protects your sender domain reputation.

What is the sender display name anti-phishing guard?

To prevent sender impersonation, display names cannot simulate domain names, IP addresses, or contain characters like @, <, >, or quotes. Hidden Unicode RTLO characters are automatically stripped.

Does open tracking break DKIM cryptographic signatures?

No. SkyRelayer injects its zero-opacity 1x1 tracking pixel into your HTML document prior to generating the RFC 822 MIME structure and signing it with your 2048-bit RSA DKIM key. This guarantees that DKIM body hashes match and pass inbox verification checks.

Can I inspect delivery events and latency?

Yes. Through the dashboard or GET /dashboardapi/emails/:id/timeline, you can inspect millisecond timestamps for each event: message initialization, pre-flight anti-spam scan results, Postfix MTA handoff, and recipient open timestamps.