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Connect Resend to Fondoo

Live6 min readUpdated

This guide sets Resend as the delivery service for the email your Fondoo site sends. Fondoo still decides who may receive each message, checks consent and suppressions, and keeps the delivery log. Resend only carries the mail. Your AI agent keeps using the normal Fondoo email operations, such as sendemail, and the messages go out through your own Resend account.

This page covers the resend delivery provider. To let your agent read your Resend domains and look up sent messages without sending anything, see the separate Resend platform guide (resend_platform).

What Fondoo can do with it

  • Send transactional and marketing email for a site through your Resend account (send_email, newsletters and support replies all use the same pipeline).
  • Use Resend for one site only, or as the default for the whole workspace. A site setting overrides the workspace setting.
  • Receive delivery, bounce, complaint, open and click events from Resend by webhook. Hard bounces and complaints add the address to your suppression list, so Fondoo stops mailing it.

Approvals and limits that still apply:

  • configure_email_provider and set_provider need the workspace owner.
  • Marketing email needs evidenced consent and a postal address set with update_email_settings.
  • An agent that sends more than 1,000 marketing emails for a site in a month needs your approval.
  • Each send_email call takes up to 100 recipients.

Before you start

  • A Resend account. Resend has a free plan and paid plans. Check Resend pricing for current volumes. Resend bills you directly. Fondoo's per-site email overage charge does not apply to mail sent through your own provider.
  • A domain verified in Resend. Resend requires at least one verified domain before you can send (Domains).
  • The same domain added and verified on your Fondoo site (set_custom_domain, then get_domain_status until it is active). Fondoo refuses to set up a sending domain it has not verified.
  • Use the same domain name in both places. Fondoo matches the From domain exactly. Resend recommends a sending subdomain such as updates.example.com. Fondoo only accepts a subdomain if that subdomain is itself a verified domain on your Fondoo site.

Step by step: get your credentials

  1. Sign in to Resend and open Domains (resend.com/domains). Click to add your domain and follow the add a domain guide. Add the DNS records Resend shows at your DNS host. Wait until Resend shows the domain as verified.
  2. Open API Keys (resend.com/api-keys) and create a new key. Resend asks for a name, a permission and an optional domain (API keys).
    • Name it something you will recognise, such as fondoo-delivery.
    • Choose Sending access. Fondoo only calls the send endpoint with this key, so it does not need full access (permission values).
    • Optionally restrict the key to your sending domain.
  3. Copy the key now. Resend does not show the key value again after you create it.
  4. Write down the list of domains you will send from, in lowercase, for example example.com. This becomes the domains list below.

You now have:

Fondoo credential fieldWhat to put in it
apiKey (required)The Resend API key from step 2
domains (required in practice)List of your verified sending domains, lowercase
webhookSecret (optional)The webhook signing secret, added in the Webhooks step

Connect it in Fondoo

In the dashboard. The Connections page lists an Email card, but it only opens setup instructions. There is no form for Resend keys yet. Use your agent or the REST API.

By asking your agent. Example prompt:

Set my site's email provider to Resend. I will run the credential step myself. Then set up example.com as the sending domain and check it.

configure_email_provider takes the key directly in its input. It has no secure paste page. Anything you paste into a chat can stay in chat logs. Prefer running that call yourself over REST from your own terminal, using an owner API key. The agent can do the other steps.

The calls, in order:

  1. configure_email_provider({siteId, provider:"resend", credential:{apiKey:"re_...", domains:["example.com"]}}). Leave out siteId to make it the workspace default.
  2. set_provider({siteId, capability:"email", provider:"resend"}). If an email provider was already selected for this site or workspace, this step decides which one is used.
  3. setup_sending_domain({siteId, domain:"example.com"}). Resend owns the DNS records, so Fondoo returns no records here. It only checks that the domain is in your domains list.
  4. check_sending_domain({siteId, domain:"example.com"}).

You can also ask your agent for connect_service({provider:"resend", siteId}). That returns a signed 15-minute link with these instructions. It never takes credentials.

REST equivalent. Every operation is POST /v1/ops/<operation>:

curl -X POST https://api.getfondoo.com/v1/ops/configure_email_provider \
  -H "Authorization: Bearer $FONDOO_OWNER_KEY" \
  -H "Content-Type: application/json" \
  -d '{"siteId":"YOUR-SITE-ID","provider":"resend","credential":{"apiKey":"'"$RESEND_API_KEY"'","domains":["example.com"]}}'

Self-hosted Fondoo uses your own API origin instead of api.getfondoo.com.

Webhooks

Webhooks let Fondoo learn about bounces and complaints. Without them, Fondoo cannot suppress bad addresses that Resend reports.

  1. Run get_email_provider({siteId}). Copy feedbackUrl. It looks like https://<fondoo email origin>/webhooks/email/resend/<providerId>.
  2. In Resend open Webhooks (resend.com/webhooks), click Add Webhook, paste the URL and select these events: email.sent, email.delivered, email.bounced, email.complained, email.opened, email.clicked (create a webhook, event types). Fondoo ignores other event types.
  3. Open the webhook's details page and copy its signing secret (verify webhooks).
  4. Run configure_email_provider again with the same scope (same siteId, or none) and the full credential, now including webhookSecret. Keeping the same scope keeps the same providerId, so the URL stays valid. Changing the scope creates a new connection with a new URL.

How signing works: Resend signs each delivery using Svix headers (svix-id, svix-timestamp, svix-signature). Fondoo checks the HMAC-SHA256 signature over the raw body with your secret (a leading whsec_ is accepted). It rejects requests more than 5 minutes old. A bounce counts as hard when Resend reports the bounce type Permanent.

Test that it works

  1. get_email_provider({siteId}) should show provider: "resend" and the scope you chose.
  2. check_sending_domain({siteId, domain}) should return verified: true.
  3. Add yourself as a contact (create_contact), then send yourself a transactional message with send_email({siteId, to, from:"hello@your-domain", subject, text, category:"transactional"}).
  4. Check list_emails({siteId}) or get_email for the status. The message should also appear in Resend's Emails list. If webhooks are set, a delivered event follows.

Troubleshooting

  • "Sender domain is not configured" or "Verify sender DNS with your provider...": the From domain is not in your domains list, or the list has a different spelling or case. Re-run configure_email_provider with the exact lowercase domain.
  • "Verify domain ownership before configuring email.": the domain is not active on your Fondoo site yet. Finish set_custom_domain and get_domain_status first.
  • "From must use the site's authenticated domain or the shared sending domain": check_sending_domain has not marked the domain verified. With Resend, Fondoo has no DNS records of its own to check, so this check may not pass in the current release. This may differ for your account. If it stays false after the steps above, contact Fondoo support.
  • "Resend send failed" in the delivery log: often a key with the wrong domain restriction, a revoked key, or a domain that is not verified in Resend. Check the key in Resend and create a new one if needed.
  • Webhook calls rejected: the secret in Fondoo does not match the webhook, or you changed the connection scope and the URL changed. Re-copy the secret, re-run configure_email_provider, and confirm the URL from get_email_provider.
  • 429 errors: Resend's default API limit is 10 requests per second per team (API reference). Fondoo already paces sends well below this.

Limits, data and security

  • Fondoo sends through a Resend connection at up to one message per second. It retries later when it hits a limit.
  • Fondoo stores the credential (API key, domains, webhook secret) encrypted, bound to that connection. get_email_provider never returns it.
  • Fondoo keeps a delivery record for each message and suppression entries for hard bounces and complaints. It reads only the event type, message ID and recipient from webhooks.
  • To rotate the key: create a new key in Resend, run configure_email_provider again with the new key, test, then delete the old key in Resend.
  • To stop using Resend: run set_provider({siteId, capability:"email", provider:"builtin"}) to go back to Fondoo's built-in delivery, then delete the API key and webhook in Resend.