Migration guide

Move from Resend to toSend.

Resend's API is the closest to ours. Most apps change the client, turn recipient strings into objects, and are done. The one thing to plan is DNS.

Start with 10,000 free emails toSend vs Resend

The plan

Run both providers side by side and move one app or site at a time. Nothing has to switch over in one go.

  1. 1

    Create a toSend account and add your sending domain. Our DKIM record (tosend._domainkey) never clashes with Resend's. Both services also use records named send: if yours already hold the values we show, keep them. If not, move a subdomain or second domain first, or use Resend's custom return path so the two stop sharing the name. We verify the domain automatically once the records are visible.

  2. 2

    Create a sending key. If an app only sends from one domain, limit its key to that domain.

  3. 3

    In one app, swap the Resend call for toSend (below), or change its SMTP settings. Keep everything else on Resend.

  4. 4

    If you handle bounces, point a toSend webhook at the same handler and map the event names from the table below.

  5. 5

    Send a test, find it in your toSend logs, then move the next app. Keep Resend until the last one has moved.

The same email, before and after

Resend (npm install resend)
import { Resend } from "resend";

const resend = new Resend(process.env.RESEND_API_KEY);

await resend.emails.send({
  from: "Your App <hello@yourdomain.com>",
  to: ["user@example.com"],
  subject: "Your receipt",
  html: "<p>Thanks for your order.</p>",
});
toSend (npm install tosend)
import { ToSend } from "tosend";

const tosend = new ToSend(process.env.TOSEND_API_KEY);

await tosend.send({
  from: { email: "hello@yourdomain.com", name: "Your App" },
  to: [{ email: "user@example.com" }],
  subject: "Your receipt",
  html: "<p>Thanks for your order.</p>",
});

If you build emails with React Email, render them to HTML in your app and pass the HTML. Batches of up to 100 work the same way on both.

Concepts

ResendtoSend
TeamTeam. Client teams share one credit balance and one invoice
Domain, with a sending regionVerified domain. The sending region belongs to the team
API key (full or sending access)Sending key, or admin key with the scopes you choose
TagsNo equivalent. Store the message_id

Send API fields

Field names already match. The differences are in the shape of addresses.

ResendtoSend
POST https://api.resend.com/emailsPOST https://api.tosend.com/v2/emails
Authorization: Bearer re_...Authorization: Bearer tsend_...
200 with {"id"}200 with {"message_id": "..."}
from: stringfrom: {"email", "name"}
to: string or array of stringsto: array of {"email", "name"}, up to 50
cc / bcccc / bcc: arrays like to
reply_toreply_to: object or "Name <email>" string
subjectsubject
html / texthtml / text (text is generated if you send only HTML)
headers: objectheaders: object of string keys and values
attachments[]: {"filename", "content"}attachments: {"name", "type", "content"}, base64, 10 MB total
tags[]No equivalent. Store the returned message_id against your own record
templateNo stored templates. Render the HTML in your app
POST /emails/batch, up to 100POST /v2/emails/batch, up to 100 emails

SMTP settings

ResendtoSend
smtp.resend.comsmtp.tosend.com
465, 2465, 587, 2587465 or 2465 (TLS), 587 or 2587 (STARTTLS)
resendAny value, it's ignored
Your Resend API keyYour toSend sending key

Webhook events

toSend sends two events, bounced and complaint, once each with no retry. Hard-bounced and complained addresses are suppressed automatically whether or not you listen.

ResendtoSend
email.bouncedbounced, with is_hard_bounce true or false
email.complainedcomplaint
email.sent, delivered, opened, clickedNot sent

Before you switch off Resend

  • Stored templates: render them to HTML in your app before sending.
  • Tags and metadata: store the returned message_id with your own record instead.
  • Open and click tracking, and delivery events: toSend doesn't have them, so remove any code that waits for them.
  • Suppression list: export it and filter those addresses out of your own lists. toSend can't import one, and starts suppressing new bounces and complaints from your first send.
  • DNS: check the send records before moving your main domain, so there's only ever one SPF record and one MX at that name.

Migration questions

Why might the send records clash?

Both services use a subdomain called send for bounce handling. A name can only carry one SPF record, so if Resend's values differ from ours, you need to pick one. If they match exactly, both work.

Does toSend have React Email support?

Not built in. React Email renders to HTML, and toSend sends HTML, so render in your app and pass the result.

Can I send from the EU like Resend's eu-west-1?

Yes. Create a team on the EU region and it sends from Frankfurt. Email logs and content are stored in the EU for every team.

Resend details from resend.com/docs, checked 28 September 2026.

Other guides: from Postmark · from Mailgun · from SendGrid · switch a FluentSMTP site · all guides

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