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Resend is a transactional email service built for developers, with a deliberately small setup: add a domain, create an API key, and send. It is a good default for a new Spree store that wants working email quickly without a long account review. Spree talks to Resend over plain SMTP, so there is nothing to install — see Emails for how the configuration works.

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Configuration

The username is the literal string resend — not your email address and not the API key. The API key goes in the password field. Resend also accepts ports 25 and 2587 for STARTTLS. Ports 465 and 2465 are implicit TLS, which Spree does not use, so stay on 587.

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Getting an API key

  1. Open the Resend dashboard and go to API Keys.
  2. Create a key with sending permission.
  3. Copy it immediately — the full value is shown only once. Keys start with re_.

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Authenticating your domain

Go to Domains → Add Domain, enter your sending domain, and add the records Resend generates at your DNS host:
  • DKIM, which proves the mail is really yours.
  • SPF, plus a record on the sending subdomain that routes bounces back to Resend.
Create each one with the type Resend displays. Older domains are given TXT and MX records for SPF, where domains added after August 2026 may get CNAME records instead — so copy what the dashboard shows rather than assuming a type. On older domains both SPF records must be right or SPF does not verify at all. Once the domain shows as verified, set SMTP_FROM_ADDRESS to an address on it. A verified domain already passes SPF and DKIM; DMARC is not needed to verify, but is worth adding afterwards.
Until you verify a domain, you can only email yourself. An unverified account sends from onboarding@resend.dev, and Resend restricts that test sender to the address on your own Resend account — anything else is refused with “You can only send testing emails to your own email address”. A store in this state appears to work while no customer ever receives an order confirmation, so verify your domain before going live.
Resend’s free tier allows 3,000 emails a month but also caps sending at 100 a day. A busy day of confirmations and shipping notices can reach that ceiling well before the monthly allowance, so check the daily figure rather than the monthly one when sizing a plan.