1Verify your domain in Resend
In Resend, open Domains, add your domain and create the DNS records it shows. Wait until the domain shows as verified.
2Create an API key
In API Keys, create a key with sending access. You’ll use it as the SMTP password.
3Enter the settings in FormSMTP
Sign up free, add a project and pick Resend as the provider so the host and port fill in.
| Provider | Resend |
| Host | smtp.resend.com |
| Port | 465 with SSL on (Resend’s recommendation), or 587 with SSL off (STARTTLS). 2465 and 2587 also work. |
| Username | resend |
| Password | Your Resend API key |
| From email | An address on your verified domain |
Click Test connection, then add your form. See the HTML contact form guide, or compare every provider on the SMTP settings page.
Common errors
- Authentication failed: the username must be exactly
resend, and the password a current API key. - Domain is not verified: the From address is on a domain that isn’t verified in Resend yet. Check its DNS records in Domains.
- Can only send to your own address: you’re sending from Resend’s shared test domain (
resend.dev), which only delivers to your account’s email. Verify your own domain.
FAQ
Which port should I use with Resend?
Resend recommends 465 (implicit TLS). If your network blocks it, use 587 with STARTTLS, or the alternates 2465 and 2587.
Do I need a verified domain?
Yes, to email anyone other than yourself. The shared resend.dev test domain only delivers to your own account address.
Why do my messages land in spam?
Usually the From address isn’t on a domain you’ve verified with the provider, or the domain has no SPF and DKIM records. Verify the domain, send from an address on it, and check the Deliverability panel in FormSMTP’s Settings.