Transactional email API

Send receipts, login codes and notifications from your app

Free for 3,000 emails a month. $15 a month for 50,000. Already on Resend? Switch by changing two environment variables.

# Send your first email
curl https://api.sendfox.com/transactional/emails \
  -H "Authorization: Bearer $SENDFOX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "Acme <[email protected]>",
    "to": ["[email protected]"],
    "subject": "Your login code",
    "html": "<p>Your code is <b>483 920</b></p>",
    "tag": "login_code"
  }'

# 202 Accepted
{ "id": "tm_4f0c9b2e7d1a5c3e8b6f2a9d", "status": "queued" }

What it is: SendFox's email API sends the one-to-one email your app triggers, like receipts, login codes, password resets and notifications. It's an HTTPS JSON API that also accepts Resend's request format. It's free for 3,000 emails a month and $15 a month for 50,000, on every SendFox plan.

Simple pricing, with a ceiling

Every address in to, cc and bcc is one email. Test addresses are free.

Free

$0 forever

3,000 emails a month
100 a day
Webhooks, logs, verified domains

Paid

$15 a month

50,000 emails a month, no daily cap
Optional overage at $0.50 per 1,000
Overage cap you set (default $50)

For comparison, Resend is $20/mo for 50,000 (checked October 13, 2026). See Resend pricing explained and the best Resend alternatives.

What you get

Resend drop-in

Set RESEND_BASE_URL and RESEND_API_KEY and your existing resend.emails.send() code sends through SendFox. No rewrite.

Its own IP pool

Transactional mail never shares an IP with marketing campaigns, so a newsletter can't hurt your login codes.

Signed webhooks

Sent, delivered, delayed, bounced, complained and failed events, HMAC-signed, retried four times. Resend's event format is one setting away.

Sandbox and test addresses

Send before you touch DNS. delivered@, bounced@ and [email protected] fake each outcome and never count against your quota.

Safe retries

Idempotency keys for 24 hours, batch sends of up to 100, and quota headers on every response.

Errors that say the fix

Every error has a stable name, a message and a fix field telling you what to change.

A bill with a ceiling

Overage is off until you turn it on, and then capped. A retry loop can't send you a surprise invoice.

Built for AI assistants

The SendFox MCP server lets Claude, Cursor and other assistants send, look up and debug emails for you.

Already on Resend?

SendFox accepts Resend's request shape, so your code stays the same. Change two environment variables, verify your domain and deploy:

RESEND_BASE_URL=https://api.sendfox.com/transactional/resend
RESEND_API_KEY=<your SendFox key>

The full switch, step by step →

Not there yet

So you can rule it out quickly:

No attachments or scheduled sends. On the Resend-compatible endpoint, requests that use them get a 422 rather than a send without them.
No SMTP. HTTPS only, so tools that can only speak SMTP can't use it yet.
No inbound email parsing.
Logs kept 30 days.

Guides for your stack

Working code for the frameworks people ask about most. Coding agent? Read the whole API as one Markdown page.

Next.jsServer actions and route handlers LaravelA mail transport for your Mailables DjangoAn email backend for password resets SupabaseAuth emails through the Send Email Hook Moving from ResendTwo environment variables

FAQ

Is the SendFox email API free?

Yes, up to 3,000 a month, 100 a day emails, on every SendFox plan including free. The paid plan is $15 a month for 50,000 emails with no daily cap.

How is an email counted?

Every address in to, cc and bcc is one email, the same way Resend counts. Emails to the sandbox test addresses are never counted.

What happens when I go over my limit?

Sends past the limit get a 429 with a clear error until you upgrade or turn on overage. Overage is $0.50 per 1,000 emails and stops at a cap you set (default $50).

Can I use it with the Resend SDK?

Yes. Point RESEND_BASE_URL at https://api.sendfox.com/transactional/resend and use your SendFox key as RESEND_API_KEY. Sends, batch sends and lookups keep working, and webhooks can use Resend's format.

Does it support SMTP or attachments?

Not yet. It is an HTTPS API only, with no attachment field, and the Resend-compatible endpoint refuses attachments and scheduled_at with a 422 rather than sending without them. If your tool can only send over SMTP, it is not a fit today.

Can I send newsletters with it?

Use it for one-to-one mail your app triggers: receipts, login codes, password resets, notifications. Newsletters go through SendFox campaigns in the same account, from a separate IP pool.

Send your first email in two minutes.

Free for 3,000 emails a month. $15 a month for 50,000. Already on Resend? Change two environment variables.

Get your free API key