The leading open-source Resend alternatives are Plunk, useSend, Postal, Reloop and FreeResend. The biggest difference between them isn't features; it's who actually delivers your mail. useSend and FreeResend send through Amazon SES, so you still depend on an AWS account. Postal runs its own SMTP server, so you own the whole path. Plunk and useSend also offer hosted plans if you want the software without running it.

This roundup covers the facts we can verify for each project, where mailbox servers like Mailcow and Stalwart fit, and when a plain Postfix server is the simpler answer.

Comparison table

Hosted pricing is as of October 2026, from third-party sources; confirm on each project's website before deciding.

Project License Hosted version (as of Oct 2026) Relies on Amazon SES? Best for
Plunk AGPL-3.0 Yes: free 1k emails/mo, then $0.001/email Check project docs Teams wanting a hosted or self-hosted platform
useSend (formerly Unsend) AGPL-3.0 Yes: from $10/mo Yes, built on SES SES users wanting a better dashboard
Postal MIT No hosted version No, its own SMTP Owning the full sending path
Reloop Apache 2.0 Check project site Check project docs Early adopters; it's newer
FreeResend MIT Check project site Yes, uses SES Keeping Resend-style API code
Mailcow — — N/A (mail server) Self-hosted mailboxes, not an API
Stalwart — — N/A (mail server) Self-hosted mailboxes, not an API

Where the table says "check", we don't have verified details and won't guess.

The projects, one by one

Plunk

Plunk is AGPL-3.0 licensed and can be self-hosted. Its hosted version, as of October 2026, includes 1,000 free emails a month and then charges $0.001 per email, which works out to $1 per 1,000. That's a useful option if you want to try the software before committing to running it yourself.

useSend

useSend, formerly called Unsend, is AGPL-3.0 licensed and built on Amazon SES. The hosted version starts from $10 a month as of October 2026. Because it uses SES underneath, you get SES's low sending cost, along with SES's account rules: sandbox, AWS-set sending limits and possible pauses for complaints. Our Amazon SES alternative page covers those trade-offs.

Postal

Postal is MIT licensed and is a full self-hosted mail platform with its own SMTP server. There's no hosted version: you run it on your own server. That makes it the most independent option here. No SES, no third-party sending service, and the IP is yours. It also means you take on everything that comes with a mail server: reverse DNS, SPF, DKIM, DMARC, warm-up, blocklists and updates.

Postal is something we can install and run for you on a VPS you own.

Reloop

Reloop is Apache 2.0 licensed and newer than the others. The Apache license is permissive, which some teams prefer to AGPL. Because it's newer, check its documentation and activity for maturity before using it in production.

FreeResend

FreeResend is MIT licensed and Resend-API compatible, and it sends through Amazon SES. Its appeal is simple: if your code is written against Resend's API, you can point it at FreeResend with little change. You trade Resend's bill for SES's, and you keep an AWS dependency.

How to choose between them

Three questions settle most decisions.

1. Do you want to stay on Amazon SES? If SES is fine and you just want a nicer layer on top, useSend and FreeResend are built for that. If the point is to get off AWS, look at Postal or a plain Postfix server, which deliver mail themselves.

2. Do you need Resend API compatibility? If you have a lot of code calling Resend's API and want minimal changes, FreeResend is designed for that. Otherwise, switching to SMTP is usually a small change, because most frameworks already support it.

3. Which license suits you? MIT (Postal, FreeResend) and Apache 2.0 (Reloop) are permissive. AGPL-3.0 (Plunk, useSend) has obligations if you modify the software and offer it over a network.

Then be honest about who will run it. Open-source software removes the license fee, not the operations work. If nobody on your team wants to watch blocklists and DMARC reports, factor that in, or compare it with self-hosted email vs Resend as a whole.

Where Mailcow and Stalwart fit

Mailcow and Stalwart come up in every self-hosted email thread, but they solve a different problem. They're mail servers for mailboxes: people receiving, storing and reading email. Your app could relay mail through them, but they aren't built as transactional email APIs.

Pick them when you need team inboxes on your own server. For app email, Postal, the API projects above, or a plain Postfix relay are better fits. Mailcow is also something we might install for a client who wants self-hosted mailboxes.

Do you need an API at all?

Many apps don't. Every major framework and language can send mail over SMTP. If your app can relay through authenticated SMTP submission on port 587, a plain Postfix server is enough. That's how we run our own mail: our apps relay to Postfix with a login, and each login can only send as its own address.

A Postfix setup has fewer moving parts than a full platform. What it doesn't give you is a web dashboard or an HTTP API. If your team needs those, Postal or one of the API projects is worth the extra complexity. Our Postfix on Ubuntu guide shows the plain setup step by step.

What every self-hosted option has in common

Whichever project you pick, if it delivers mail itself, the same jobs fall to you:

  • Port 25. Many clouds block outbound port 25 by default. AWS does; OVH didn't in our case. Check your provider.
  • DNS. SPF (with its 10-lookup limit), DKIM with 2048-bit keys, DMARC and a PTR record that matches your mail hostname. See our reverse DNS guide.
  • Warm-up. New IPs have no reputation. Start with tens of emails a day and build up over two to six weeks. Our IP warm-up guide has a plan.
  • Monitoring. DNS drift, blocklists, TLS expiry, the mail queue and DMARC reports.

The software is free. Running it well takes ongoing attention.

Open source vs a managed server

Self-host an open-source project Our Server Setup Our Managed Server
Software cost Free Included Included
Our fee None $499 one-time $499 setup + $99/month
VPS Yours, typically $5–20/mo Yours, typically $5–20/mo Yours, typically $5–20/mo
Who sets it up You We do We do
Who watches it You You, from our runbook We do, daily

All prices are on the pricing page. Our standard build is Postfix with OpenDKIM, SRS, TLS and fail2ban; if you'd rather have Postal, we can install and run that for you instead.

If you send 250,000 or more emails a month and don't want a server to look after at all, our hosted Scale plans (from $149 a month) give you a dedicated server and IP with a Resend-style API. Scale plans are in early access; see high-volume email sending.

When to stay on Resend

If you send under roughly 100k emails a month, Resend at $20–35 a month as of October 2026 is cheaper than running and watching a server, open source or not. Self-hosting starts paying off on cost above roughly 200k emails a month. See our Resend alternative page for the full cost comparison.

The bottom line

Open-source Resend alternatives are a real option, and the right one depends mostly on whether you want to stay on SES. FreeResend and useSend keep SES underneath. Postal gets you off it entirely. A plain Postfix server is the lightest option if you don't need an HTTP API.

Want one of these installed and run for you? See Server Setup and Managed Server pricing, or email hello@ownmailserver.com.