Mailinator is the tool most QA engineers reach for first, and for a public throwaway inbox it is genuinely fast. The friction shows up the moment your test needs a private inbox or an API: those live on the paid Team and Enterprise plans, and the free tier's inboxes are public to anyone who guesses the address. This post compares the alternatives a developer actually evaluates: Mailosaur, MailSlurp, Mailtrap, Ethereal, GreenMail, and our own TempMaily, with an honest note on what each is best at and who should skip it.
We run a disposable-mail service with an API, so read the TempMaily section as an operator making its own case, not a neutral verdict. Everywhere else we describe the model rather than invent numbers, because competitor pricing shifts and a fake precise figure helps nobody. If you are a consumer looking for a throwaway inbox to dodge marketing email rather than a developer wiring up tests, the best temp mail alternatives roundup is the page you want instead.
Quick answer
Reach for Mailosaur when you want a commercial, well-documented API with real inboxes plus SMS and you can pay for it. Reach for MailSlurp when you want an API-first service with a large free allowance. Reach for Mailtrap when the thing you are testing is your app's outbound mail, not inbound codes. Reach for Ethereal when you just need a disposable SMTP account to preview a message during development. Reach for GreenMail when the whole test must run self-hosted inside your CI. And reach for TempMaily when you want lightweight REST polling, a fresh disposable inbox per test, an MCP server for AI agents, and flat pricing instead of an enterprise quote.
What Mailinator gets right, and where it stops
Mailinator earned its place. Type any name at @mailinator.com, and the inbox exists — no signup, no inbox creation call, and a clean web UI that renders the message. For a manual smoke test of "did the signup email send at all", it is hard to beat. The limits are structural, and every one is a reason a QA developer eventually migrates:
- Free inboxes are public. Any address on the shared free domain is readable by anyone who types it into the web UI, so a verification code your test received is visible to the world while it sits there. Fine for a throwaway smoke test, wrong for a real credential.
- Private domains and the API cost real money. Private inboxes, private domains, and programmatic access sit behind the Team and Enterprise plans. You go from $0 to a monthly bill measured in the tens-to-hundreds as of mid-2026 the moment you need a private address in CI.
- No self-hosted option. If your CI network rules say test mail cannot leave your infrastructure, Mailinator is out before you compare features.
- It receives, it does not sandbox your sender. Mailinator is an inbound inbox. If you need to trap the mail your app sends and inspect its HTML, that is a different tool.
None of that makes Mailinator bad. It makes it a specific shape, and the alternatives below each bend that shape in a direction it won't.
What to compare
These are the axes that decide whether an email-testing tool fits your suite. They matter more than the marketing feature list.
- Free tier you can test in five minutes. Can you go from landing page to a passing API call without a sales call or a credit card? For a developer evaluating tools, a testable free tier is the whole decision, not a footnote.
- Public vs private inboxes. Is a received message readable by strangers, or scoped to your key? Public inboxes are fine for smoke tests and disqualifying for anything with a real token in it.
- A real REST API with docs. You are automating, so you need documented endpoints to create an inbox, list messages, and read a body, not a webpage to scrape.
- Inbound vs outbound model. Some tools receive mail sent to an address (Mailinator, Mailosaur, MailSlurp, TempMaily). Others trap mail your app sends (Mailtrap, Ethereal). Picking the wrong half is the most expensive mistake on this page.
- Self-hosted option. Can it run entirely inside your CI with no external dependency? Only GreenMail says yes, and for some teams that single column decides it.
- Pricing shape. Flat, usage-metered, or an enterprise quote? A per-test inbox on a flat plan budgets very differently from a metered API.
No tool wins every column. The list below is honest about where each lands.
The alternatives, one by one
Mailosaur
What it does well: A commercial email-and-SMS testing platform built for exactly this job. You get real inboxes on virtual servers, a well-documented REST API, SMTP capture, webhooks, and helper libraries for most test frameworks. It handles both directions — receive an inbound code, or capture what your app sends and assert on its spam score and HTML. For a team that wants one paid, supported tool covering email and SMS, it is the safe institutional pick.
Who should skip it: It is a paid product with a trial, not a free-tier-forever tool. If you want something to wire into a side project for free, Mailosaur is more platform than the task requires.
MailSlurp
What it does well: API-first to the core, with a genuinely usable free allowance. You create inboxes programmatically, receive real inbound mail, and read it over a REST API, with SDKs across many languages plus SMTP and webhook support. It leans developer, not marketer, and the free tier lets you prove the flow works before you pay. It also covers phone-number and SMS inboxes.
Who should skip it: The free tier has meaningful caps, and heavy parallel CI use pushes you onto a metered plan whose cost tracks your inbox and request volume. If you want flat billing rather than usage-metered, watch the meter before you commit.
Mailtrap
What it does well: The best-known email sandbox. Point your app's SMTP at Mailtrap in staging and every message it sends is trapped in a fake inbox instead of reaching a real recipient. You then inspect the HTML, check spam score, preview across clients, and assert via its API that the right mail went out. For testing your own transactional templates without emailing real users, this is the right model, and there is a free tier.
Who should skip it: It is fundamentally about outbound — mail your app generates. If your test needs to receive a code from a third-party service at a real inbox, the sandbox is the wrong half of the problem.
Ethereal (Nodemailer)
What it does well: A free, zero-commitment fake SMTP service from the Nodemailer author. Call nodemailer.createTestAccount() and you get throwaway SMTP credentials; anything you send lands in an Ethereal web preview instead of a real inbox, and the send response hands you a preview URL. For confirming during local development that your mail renders and sends, with no signup, it is frictionless.
Who should skip it: Ethereal never delivers mail and has no inbound path, so it cannot receive a verification code from your app under test. Treat it as a development preview tool, not a way to assert a real signup flow end to end.
GreenMail
What it does well: The self-hosted answer. GreenMail is an open-source, in-memory mail server speaking SMTP, POP3, and IMAP that you start inside your test process (famously as a JUnit rule in JVM projects), so the whole exchange happens on the machine with no external call. It is free, deterministic, and fast, and nothing leaves your CI network. When policy forbids test mail touching the public internet, this is the tool.
Who should skip it: Because it lives inside your process, it only tests your own send path. It cannot receive mail from an external sender or verify real-world deliverability — there is no outside world in a GreenMail test. It also skews JVM; outside Java the ergonomics are rougher.
TempMaily (us)
What it does well: A disposable inbox reachable over a small REST API, built for the create-poll-extract-assert loop. POST /inboxes mints a fresh address scoped to your key (not a public inbox), GET /inboxes/{id}/messages lists what arrived, and GET /messages/{id} returns the full bodyText and bodyHtml to run a code regex over. Inbox lifetime is a parameter (expiry of 1d, 7d, 30d, or never), so a per-test inbox and a long-lived one are the same endpoint. The key is Bearer-authenticated and xtm_-prefixed, the rate limit is 300 requests per 60 seconds, and there are signed HMAC-SHA256 webhooks when you would rather be pushed than poll. An MCP server exposes the same six operations as tool calls, so an AI agent can own an inbox directly. Pricing is one flat Premium plan at $9.90 per month, API and MCP included, not a separate enterprise tier. Working Cypress and Playwright examples ship in the docs.
Who should skip it: The API and MCP server are Premium-only; the free inbox is a no-signup browser tool, so there is no free programmatic tier to test in CI the way MailSlurp offers. We do not capture your app's outbound SMTP, so a sender's sandbox for your own templates is a job for Mailtrap or Mailosaur. And we are hosted, so fully self-hosted mail is GreenMail's answer, not ours. We are built for inbound REST polling and per-test disposable inboxes, and we would rather say so than pretend to be every tool here.
Comparison table
| Tool | Free tier | Private inboxes | REST API | Self-hosted | Starting price |
|---|---|---|---|---|---|
| Mailinator | Yes, public inboxes | Paid plans only | Paid plans only | No | Free public; paid private (tens–hundreds/mo) |
| Mailosaur | Trial only | Yes | Yes, well-documented | No | Paid, commercial tiers |
| MailSlurp | Yes, with caps | Yes | Yes, API-first | No | Free tier; usage-metered paid |
| Mailtrap | Yes | Yes (sandbox) | Yes | No | Free tier; paid scales |
| Ethereal | Yes, free | Ephemeral test accounts | Preview only, no inbound | No | Free |
| GreenMail | Free (open source) | Local only | Via IMAP/POP3, no hosted API | Yes | Free |
| TempMaily | Free browser inbox | Yes, key-scoped | Yes, Premium | No | $9.90/mo flat |
Competitor details change over time, so treat the non-TempMaily rows as a mid-2026 general picture rather than a guarantee. Where an exact figure moves often, the table names the model instead of a number.
Which one for which job
Skip the deliberation and match the tool to the mail flow:
- Receive a real inbound verification code in an E2E test. Use an API-first inbox: MailSlurp for a free start, Mailosaur for a supported commercial platform, or TempMaily for flat pricing and a per-test disposable inbox. The pattern is identical across all three — create, poll, extract, assert.
- Inspect the mail your own app sends. Use Mailtrap's sandbox or Mailosaur's SMTP capture. You are checking your outbound template, spam score, and rendering, so you want a trap, not an inbox.
- Preview a message during local development. Ethereal, in two lines of Nodemailer. No signup, a preview URL, done.
- Keep everything inside CI with no external call. GreenMail, started in-process and fully deterministic.
- Give an AI agent its own inbox. TempMaily's MCP server exposes inbox creation and mail reading as tool calls, so an agent handles the signup flow without custom HTTP code.
Common mistakes
A few errors show up again and again when teams migrate off Mailinator:
- Testing an inbound flow with an outbound tool. Pointing a signup-code test at Mailtrap or Ethereal fails because neither receives external mail. Confirm your test's direction before you pick the tool.
- Shipping a public inbox into a real test. A public Mailinator inbox holding a live token is readable by anyone. If the code matters, use a key-scoped private inbox.
- Hardcoding one shared inbox across tests. The instant you shard across parallel machines, two tests read each other's mail. Create a fresh inbox per test and tear it down afterward — the Cypress example does exactly this.
- Matching any digits as the code. A bare
\d{6}regex catches a copyright year or an order number before the real OTP. Anchor the pattern to nearby copy like "your code is".
The honest bottom line
If Mailinator's public inboxes or the price of its API pushed you here, the replacement depends on what you are actually testing. Receiving real inbound codes over an API on flat pricing is where TempMaily fits, and we have been straight above about where it does not: no outbound sandbox, no self-hosting, no free API tier. Testing your own sender wants Mailtrap or Mailosaur; running fully self-hosted wants GreenMail; a quick local preview wants Ethereal. When your flow is inbound REST polling with a disposable inbox per test, read the API reference, skim the test-address guide for QA, and compare the Premium plan — then delete the flaky "we skip email in CI" line from your test plan.