Migrating from Resend

SpacePost implements the Resend API: same paths, same field names, same response shapes and the same error format. Most apps migrate by changing a base URL and an API key.

1. Create a SpacePost API key in the dashboard. SpacePost keys start with sp_live_ (Resend keys start with re_).

2. Add and verify your domain in SpacePost. DNS records differ from Resend’s, so add the new DKIM CNAMEs and the send MX/TXT records. You can keep Resend’s records in place while you cut over, because DKIM selectors do not collide. See Adding and verifying. Move your SPF/DMARC policy only if you changed the send subdomain.

3. Switch the client. Pick one of the options below.

   Resend SDK, unchanged

   Keep the official resend package. Set the base URL with an environment variable and use your SpacePost key:

   .env

   RESEND_API_KEY=sp_live_YOUR_API_KEY
   RESEND_BASE_URL=https://api.spacepost.dev

   import { Resend } from "resend";
   
   const resend = new Resend(process.env.RESEND_API_KEY);
   await resend.emails.send({ from: "Acme <hello@acme.com>", to: "you@example.com", subject: "Hi", html: "<p>Hi</p>" });

   Or pass it in code:

   const resend = new Resend("sp_live_YOUR_API_KEY", { baseUrl: "https://api.spacepost.dev" });

   @spacepost/node

   Swap the import. The method names and { data, error } return shape are the same.

   import { Resend } from "resend";
   const resend = new Resend(process.env.RESEND_API_KEY);
   import { SpacePost } from "@spacepost/node";
   const spacepost = new SpacePost(process.env.SPACEPOST_API_KEY);
   
   await resend.emails.send({ ... });
   await spacepost.emails.send({ ... });

   Raw HTTP / other languages

   Change the host and the key. Paths and bodies are identical.

   curl https://api.resend.com/emails -H "Authorization: Bearer re_..."
   curl https://api.spacepost.dev/emails -H "Authorization: Bearer sp_live_..."

   SMTP

   Change host, port and password, and use STARTTLS. The username resend is accepted as an alias for spacepost.

   Host: smtp.spacepost.dev    Port: 25976 (STARTTLS)
   User: spacepost             Password: sp_live_YOUR_API_KEY

4. Recreate your webhooks. Create each endpoint again in SpacePost (POST /webhooks) and store the new signing_secret. Verification code written for Resend or Svix keeps working because SpacePost sends the same Standard Webhooks headers (plus svix-* duplicates). See Verifying signatures.

5. Move audiences and contacts. Create audiences and import contacts through POST /audiences/{id}/contacts. Placeholders such as {{{FIRST_NAME|fallback}}} and {{{RESEND_UNSUBSCRIBE_URL}}} work unchanged in broadcasts.

6. Send a test, then cut over. Send to delivered@test.spacepost.dev, check the webhook arrives, then deploy.

Parity table

Resend feature	SpacePost	Notes
POST /emails	Supported	to/cc/bcc/reply_to up to 50 each; camelCase aliases replyTo, scheduledAt accepted
POST /emails/batch	Supported	Up to 100 emails; attachments and scheduled_at are allowed per email; all-or-nothing
GET /emails/{id}, GET /emails	Supported	List omits bodies
PATCH /emails/{id}	Supported	Reschedule scheduled emails
POST /emails/{id}/cancel	Supported	Scheduled emails only
Attachments (content, path)	Supported	path must be https
Tags, custom headers	Supported	Same constraints on tag characters
Idempotency-Key	Supported	24 hours, POST /emails and /emails/batch
Domains (create, get, list, verify, update, delete)	Supported	open_tracking, click_tracking
API keys	Supported	full_access, sending_access, optional domain_id
Webhooks, Standard Webhooks signing	Supported	Also svix-* headers
Audiences, contacts, broadcasts	Supported	Contacts live under /audiences/{id}/contacts
Suppressions API	Supported	Extra: list, add and remove entries
Tenants (platform mode)	SpacePost only	Isolated reputation per customer; see Platform mode. The Resend SDK drops tenant_id; use resend.post or tenant-owned domains
SMTP relay	Supported	smtp.spacepost.dev:25976 with STARTTLS (no implicit TLS on 465 yet)
Inbound email	Not yet
Templates editor	Not yet	Use React Email or your own HTML

Differences to know about

Key prefix

SpacePost keys start with sp_live_. A re_... key is rejected with 403 invalid_api_key. If you see that error after migrating, an old RESEND_API_KEY is still deployed somewhere.

• last_event values. Resend’s values (queued, scheduled, sent, delivered, delivery_delayed, bounced, complained, opened, clicked, canceled, failed) are all present. SpacePost adds suppressed, used when every recipient was on your suppression list. Status never moves backwards: an opened event arriving before delivered keeps the later state.
• Extra webhook event. email.suppressed fires when a recipient is skipped because it is suppressed. Subscribe only to the events you handle. Payloads are otherwise identical to Resend’s; data.tenant_id is added for tenant mail.
• Rate limit. 10 requests per second per team (25 on Scale) versus 2 on Resend, with the same ratelimit-* headers.
• Pricing. Pro is €9 for 50,000 emails with €0.25 per extra 1,000, billed in EUR excluding VAT (Resend Pro: USD 20 with USD 0.90 per extra 1,000, Resend’s USD prices as of 23 October 2026). After the first 7 days every plan, including Free, has a daily cap that grows with your sending: the larger of 1,000 and twice your best day in the last 14 days, up to 50,000 per day. See Plans and quotas.
• What counts as an email. Every recipient counts: one email to 3 recipients (to, cc and bcc together) counts 3 against your quota.
• Test sender. onboarding@test.spacepost.dev replaces onboarding@resend.dev. Test inboxes live at test.spacepost.dev instead of resend.dev: delivered@, bounced@, complained@, delayed@, plus softbounced@ (SpacePost only).
• New-account sandbox. The first 7 days are limited to 100 emails per day. See Verification and limits.
• Automatic pausing. Teams with abnormal bounce or complaint rates are paused automatically. See Automatic pausing.
• Base URL. https://api.spacepost.dev, with paths at the root. A /v1 prefix is also accepted (https://api.spacepost.dev/v1/emails).