Resend SendGrid Migration — check your code for free

Eight SendGrid lines break on Resend in order-mail.js, a Node.js receipt mailer with a bounce webhook, and a developer moving off Twilio SendGrid gets no error from any of them.

Migrate from Twilio SendGrid to Resend: the lines that fail silently

Twilio SendGrid retired its free Email API plan starting May 27, 2025 (Twilio changelog: "Changes coming to SendGrid's Free Plan"). New accounts have had a 60-day trial since March 25, 2025, and the paid Essentials plan starts at $19.95 a month. Resend keeps a free tier of 3,000 emails a month and a send call that looks almost the same, so plenty of teams are switching.

The send call is the easy part. sgMail.send(msg) becomes resend.emails.send({...}). The trouble is the fields that have no Resend twin. They do not throw. They are dropped, and the mail behaves differently.

What the check found in order-mail.js

Resend Migration Check ran its 18 rules over the sample file and returned eight findings:

The migrated file, with new Resend(process.env.RESEND_API_KEY), an ISO scheduledAt, tags and a type === 'email.bounced' branch, returns zero.

The three that cost the most

sandboxMode. In SendGrid, mailSettings.sandboxMode.enable validates a message without delivering it. Resend has no such field. Keep the block after the switch and your staging environment sends real receipts to real customers. Resend's answer is test addresses such as [email protected].

asm groupId. SendGrid's unsubscribe groups (asm) stop mail to people who opted out of one kind of message. resend.emails.send has no field for it, so the group is ignored and the opted-out address gets the email. You need your own suppression check before sending.

event === 'bounce'. SendGrid's Event Webhook posts an array of objects with an event field: bounce, spamreport, deferred. Resend posts one object with a type field: email.bounced, email.complained, email.delivery_delayed. An if (e.event === 'bounce') branch never runs again, and bounced addresses stay on your list. The signature header changes too: Resend signs with Svix (svix-id, svix-timestamp, svix-signature) instead of X-Twilio-Email-Event-Webhook-Signature.

Why find-and-replace is not enough

Find-and-replace swaps @sendgrid/mail for resend and setApiKey for a constructor. It does not know that sandboxMode, asm and the webhook event names have no Resend field. The code still compiles and runs. That is why each finding here names the Resend line, or says plainly that there is none.

Python too

The same rules read Python. from sendgrid import SendGridAPIClient, SendGridAPIClient(os.environ["SENDGRID_API_KEY"]) and message.send_at = 1735689600 are flagged, and a hard-coded send_at is compared with the check date you set: on 2026-09-29 that timestamp (2025-01-01) is already in the past.

Try it

Search "resend migration check" in VS Code or Open VSX and run it on the open file. The free check has no key and no limit. The full version exports a workspace-wide migration plan, file by file.