Resend vs Mailgun

Monthly cost at 10,000, 50,000, 100,000 and 500,000 emails

At 10,000 emails, Mailgun is $5 a month cheaper. Its pricing page lists Basic from $15 with 10,000 emails, and Resend's pricing page starts paid sending at Pro, $20 a month with 50,000 emails. That is $180 a year against $240. Resend's Free plan does cover 3,000 emails a month, so a pre-launch product can stay at $0 longer than on Mailgun, where Free is 100 a day.

At 50,000 the order reverses. Resend Pro is $20 a month ($240 a year) and Mailgun Foundation is $35 ($420 a year), a $15 monthly gap. Foundation's first month is free, which trims the first-year total to $385, still $145 above Resend. At 100,000 emails Resend Pro reads $35 ($420 a year) and Mailgun Foundation reads $75 ($900 a year), a $40 gap. If you take the higher plan on both, Scale is $90 a month on each, which is $1,080 a year, so that comparison is about features alone.

At 500,000 emails Resend Scale reads $350 ($4,200 a year) and Mailgun Scale $400 ($4,800), a $50 monthly gap and $600 a year. Add the extras you need: a Resend dedicated IP is $30 a month, so $380, while Mailgun Scale already includes one IP at $400. Resend's slider also shows extra emails at $0.70 per 1,000 at this stop, while Mailgun lists Scale overage from $1.10 per 1,000. Between published points, neither vendor gives a rule that supports a price, so ask for a quote when your volume sits between two readouts.

The send call: idempotency, batches, templates and limits

Resend's send email reference is a single JSON POST. It supports an Idempotency-Key header (unique per request, valid for 24 hours, up to 256 characters) so a retried request will not send twice, scheduled_at in natural language or ISO 8601, tags as name and value pairs, and attachments up to 40 MB per email after Base64 encoding. A template is sent by id or alias with variables; passing html, text or react alongside a template is a validation error, and a missing variable fails the call. The batch endpoint accepts up to 100 emails but does not support attachments yet. The default rate limit is 10 requests per second per team.

Mailgun handles bulk differently. Its batch sending guide allows up to 1,000 recipients in one call when you pair the to list with recipient-variables, a JSON object keyed by address that you reference as %recipient.name% inside the message. Without it, everyone sees everyone else's address. Stored templates use Handlebars with if, unless, each, with and equal helpers, and the templates guide caps an account at 100 templates and 40 versions each, created separately per region.

For a product that sends one message per event (a receipt, an invite), both calls are one request and the difference is minor. For a nightly digest to 30,000 users, Mailgun needs 30 calls with 1,000 recipients each, while Resend's batch endpoint needs 300 calls of 100, which at the default limit of 10 requests per second is at least 30 seconds of calls.

Webhooks: Svix headers against an HMAC token

Resend webhooks are signed with Svix. Per its verification guide, each request carries svix-id, svix-timestamp and svix-signature headers; you pass them with the raw body and the endpoint's signing secret to the Resend SDK's verify method or to the Svix package, and it throws when the signature is wrong. The guide warns that parsing JSON and re-serialising the body breaks the check. The retry schedule has eight attempts, any message can be replayed from the dashboard, and a persistently failing endpoint is switched off with an email to your team.

Mailgun's signature scheme sends a 50-character token, a timestamp and a hex signature inside a signature object next to the event data; you join timestamp and token and compute an HMAC-SHA256 with the account-wide Webhook Signing Key. A 200 response ends delivery, a 406 rejects it without retrying, and any other response is retried over 8 hours per the retry page.

In practice the Resend flow is quicker to write, because one library call does the verification and the dashboard replay button helps during development. The Mailgun flow is a short function you own, and its 8-hour retry window is enough to cover a long deploy outage. Resend's schedule stretches over more than 27 hours (5 seconds, 5 minutes, 30 minutes, 2 hours, 5 hours, then 10 hours twice), so a weekend-long outage is the case that needs a replay on either side.

Receiving mail: fetch it yourself or route it on arrival

Resend's receiving documentation offers two addresses: any username at a Resend-managed id.resend.app subdomain, or any address at your own domain once you add an MX record. Resend parses each message and posts to the endpoint you chose; the full HTML, text and headers are retrieved afterwards through the API, and attachments come as metadata with temporary download URLs. Forwarding and threaded replies are supported. The numeric limits (size, retention) are not on that page, so read the linked guides before you plan around large attachments.

Mailgun's routes evaluate every incoming message against ordered filters (match_recipient, match_header, catch_all) and run actions: forward to an address or URL, store, or stop. Priority runs lowest first, and a stop prevents later routes from firing. A forward to a URL ending in json arrives as application/json with the signature fields moved into headers; any other URL gets form data.

Choose Resend receiving when inbound is a single feature (parse a reply, attach it to a record) and you are happy to make a second call for the body. Choose Mailgun routes when different addresses mean different behaviour and you want the dispatcher outside your own code.

Validation, suppressions and a marketing tab

Mailgun's validation API returns deliverable, undeliverable, do_not_send, catch_all or unknown with a risk level, and flags disposable and role-based addresses. Resend lists no validation endpoint, so a team that needs to filter signups either keeps a separate validator or leans on Resend's automatic suppression. The suppression list is team-wide across domains and applies to both transactional and broadcast mail; hard bounces and spam complaints land there automatically, you can add addresses manually or by CSV, and a webhook fires on suppression.added, suppression.removed and email.suppressed. Removing an address does not guarantee delivery, because a second bounce re-adds it.

Resend's Marketing tab prices broadcasts and automations by contact count: free at 1,000 contacts with 10,000 automation runs and 3 segments, then $40 at 5,000, $80 at 10,000, $180 at 25,000, $250 at 50,000 and $450 at 100,000. Its broadcasts documentation sends to a segment of your contacts and tracks delivery, click and open rates when tracking is enabled. A SaaS that wants product announcements next to transactional mail can stay on one vendor; Mailgun's pricing page lists sending plans, so an announcement tool there would be a separate purchase.

Moving from Mailgun to Resend

Keep a validation step if you used Mailgun's: nothing on Resend's pricing page replaces it. Run both vendors in parallel on a low-risk stream, such as password resets, before moving billing and invite email.

1. Add your sending domain in Resend and publish its DNS records. Resend recommends sending from subdomains to isolate reputation, so use one for transactional mail and another for newsletters.
2. Create an API key. If you used Mailgun SMTP, switch to smtp.resend.com with the username resend and the API key as the password, on ports 25, 465, 587, 2465 or 2587.
3. Map the payload: Mailgun o:tag values become tags as name and value pairs (ASCII letters, digits, underscores and dashes), v: variables become template variables, and recipient-variables batches become arrays of up to 100 message objects. The batch endpoint rejects attachments, so send those individually.
4. Rebuild Handlebars templates as Resend templates, taking care that FIRST_NAME, LAST_NAME, EMAIL and UNSUBSCRIBE_URL are reserved variable names. A message that uses a template cannot also pass html, text or react.
5. Replace the HMAC check with Svix verification using the raw body, and map Mailgun events to Resend ones: delivered to email.delivered, temporary_fail to email.delivery_delayed, permanent_fail to email.bounced, complained to email.complained.
6. Replace routes with receiving: add the MX record (or use an id.resend.app address), subscribe to email.received, then fetch the body and attachments by API. Port any priority or catch-all logic into your handler.
7. Export Mailgun's bounce, complaint and unsubscribe lists and add them to Resend's suppression list, up to 100 addresses per API call. Add an Idempotency-Key to retried sends and respect the 10 requests per second limit during bulk jobs.

Moving from Resend to Mailgun

1. Choose US or EU for the account, add each sending domain and publish the DNS records Mailgun gives you. Create the templates in the same region you will send from.
2. For SMTP use smtp.mailgun.org with per-domain credentials; port 587 is Mailgun's suggestion. For the API, use the key against the messages endpoint for the domain.
3. Render React Email components to HTML in your own code, because Mailgun has no react parameter, then upload templates as Handlebars or send HTML directly. Mind the 100-template and 40-version cap.
4. Convert Resend batches of 100 messages into one call with up to 1,000 recipients and recipient-variables, if the message body is the same. If every message differs, keep one call per message.
5. Replace Svix verification with the HMAC check: join timestamp and token and compare with the signature. Map email.bounced to permanent_fail, email.delivery_delayed to temporary_fail and email.complained to complained.
6. Rebuild receiving as routes, with a forward action to your URL and a stop on specific recipients. Export Resend's suppression list and import unsubscribes and complaints by CSV (up to 25 MB).
7. Add your own send ledger: the Mailgun send documentation read for this comparison describes no idempotency header, so retries must be made safe in your database. If you also used Resend's Marketing tab, plan a separate home for contacts and broadcasts, since Mailgun's pricing page lists sending plans only.