Mailbay vs Mailosaur
Mailosaur is a testing tool: email and SMS, previews, spam checks and SDKs for every test framework. Mailbay covers the email part of that and also sends real mail.
Updated 3 min read
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In short
Mailosaur is a testing product, and a thorough one: email and SMS, extracted codes and links, spam and deliverability reports, previews across mail clients, and SDKs for every popular test framework. Mailbay is email infrastructure that happens to be good at the core of email testing: catch-all addresses and a blocking wait that returns the code. It also sends real mail, which Mailosaur does not.
Pick Mailosaur if
- You test SMS codes as well as email, or need a virtual TOTP authenticator.
- You want rendering previews, accessibility checks or spam reports on your emails.
- Your team wants a ready made SDK for Cypress, Playwright, Selenium or WebdriverIO.
Pick Mailbay if
- You only need email, and want it free while you build.
- The same inboxes should work for AI agents in production, not only in CI.
- You also want to send your app's real email from the same account.
Who each is for
Mailosaur is for QA and engineering teams. Every inbox has its own domain where any address works, such as anything@abcd1234.mailosaur.net [2], and codes are extracted from emails and texts [3]. Sending is limited to testing: you can only send to verified external addresses [6].
Mailbay is for developers and agents. Each workspace has a private {code}.mailbay.email domain with a Catch-all, so test-8121@k7m3qz.mailbay.email works without setup, and the same project can send production mail from your verified domain.
Features and prices
Mailbay is in private beta and free while it runs. The Mailbay prices below are the planned plans from our pricing page; billing is not live yet.
| Feature | Mailbay | Mailosaur |
|---|---|---|
| Entry price | Free plan: 3 inboxes plus the Catch-all, 3,000 sent emails a month | Personal from $20 a month billed annually, 14 day trial [1] |
| Team plan | Pro, $9 a month | Core from $50 a month billed annually, 5 seats [1] |
| Catch-all addresses | Yes, on your private mailbay.email code | Yes, per inbox [2] |
| Codes and links extracted | Yes, returned by wait | Yes [3] |
| Block until the email arrives | Yes: API, CLI and MCP | Not stated |
| SMS testing | No | Yes, as an add on [1] |
| Spam and deliverability reports | Spam score on received mail (rspamd) | Deliverability report and SpamAssassin [4] |
| Client previews | No | Add on [1] |
| Test framework SDKs | None; plain HTTP from any framework | Cypress, Playwright, Selenium, WebdriverIO and more [5] |
| Sending real email | Yes, from your verified domain over API or SMTP | Only to verified addresses [6] |
| MCP server | Yes | No first party server found |
Sources, read on October 14, 2026
- [1]Mailosaur pricing: mailosaur.com/pricing
- [2]Mailosaur, sending to Mailosaur: mailosaur.com/docs/email-testing/sending-to-mailosaur
- [3]Mailosaur, codes: mailosaur.com/docs/automation/codes
- [4]Mailosaur, spam checks: mailosaur.com/docs/automation/spam
- [5]Mailosaur, API and SDKs: mailosaur.com/docs/api
- [6]Mailosaur, sending from Mailosaur: mailosaur.com/docs/email-testing/sending-from-mailosaur
Prices change. If something here is out of date or wrong, email hello@mailbay.dev and we will fix it.
Where Mailosaur is better
- SMS and authenticator codes. If your sign up sends a text or uses TOTP, Mailbay cannot help.
- Email quality checks. Previews across clients, accessibility testing and spam reports are things Mailbay does not do.
- Framework SDKs. A Cypress plugin or Playwright helper is less code than an HTTP call, and Mailosaur has them for most frameworks.
Where Mailbay is better
- Cost. Free during the beta, and the planned free plan stays free with unlimited Catch-all addresses.
- Beyond CI. The inbox your test suite uses can be the inbox an agent uses in production, with threads, replies and webhooks.
- Real sending. Test the email your app sends, then send it for real from the same project.
Moving tests from Mailosaur
Most suites use two calls: make an address, wait for the message. In Mailbay the address needs no call at all, and the wait is one request. The full Playwright example is in the catch-all testing guide.
- Replace
anything@SERVER_ID.mailosaur.netwithanything@CODE.mailbay.email. Your code is inGET /v1/measshared_domain. - Replace the SDK's wait call with a request to the Catch-all inbox, filtered by the address the test used.
- Read
codes[0]orlinks[0]from the answer.
const res = await fetch(
`https://api.mailbay.dev/v1/inboxes/${CATCH_ALL_ID}/wait?to=${encodeURIComponent(address)}&timeout=60`,
{ headers: { Authorization: `Bearer ${process.env.MAILBAY_API_KEY}` } },
);
const { codes, links } = await res.json();Read next
- Catch-all inboxes for end to end testsEmail is the step most end to end suites skip, because it is slow and flaky to check. A catch-all domain makes every test its own address, and a blocking wait removes the polling.
- An email inbox for your AI agentAn agent that signs up for things needs an address that receives mail, and a way to get the code out of it without polling. Here is the whole flow in three steps.
- Mailbay vs AgentMailBoth give agents their own inboxes over an API and MCP. AgentMail is further along; Mailbay adds sending for apps, a support inbox and custom domains on the free plan.
Join the beta
Mailbay is in private beta and free while the beta runs: inboxes, sending, your own domains and MCP. We invite people in small batches and read every note on the form.