Mailosaur alternative: GrabMail vs Mailosaur

At a glance

Fourteen rows. Every Mailosaur cell is what its pricing page, FAQ and documentation said on 2 September 2026; every GrabMail cell is read from the constants the service enforces. “Partly” means a paid tier, a cap, or a caveat the row cannot hold — the sections below say which.

Checked 2 September 2026. Mailosaur publishes annual-billing prices (“from $20 per month, billed annually”) and a “Save 20%” toggle, but not the monthly-billing figure; prices exclude VAT, which is 20% for UK customers. Its retention maximum per plan is described but not given as a number of days.

What Mailosaur does well

Mailosaur is what a QA team buys when email is one of several channels it has to test. Four things it does that GrabMail does not:

• Private inboxes, each with unlimited addresses. Every inbox gets its own subdomain, INBOX_ID.mailosaur.net, and any local part on it works with nothing to configure. Messages are visible only inside that inbox. On GrabMail, any name works too — but anyone who knows it can read it.
• SMS, 2FA and previews. Phone numbers for SMS codes, a virtual authenticator for TOTP, and real-device previews of how a message renders. These are add-ons from $37.50 and $25 a month, and they have no equivalent here.
• Mail clients and rules. POP3 and IMAP on Core and above, auto-forwarding rules, and replying or sending to external addresses. GrabMail is HTTPS-only and receive-only.
• Certificates and ceilings. ISO 27001:2022, PCI DSS, GDPR and CCPA, and a hard daily limit that can never turn into a surprise invoice: “you cannot go over your limit without prior agreement”. GrabMail has no certificate and no SLA.

Where GrabMail is different

GrabMail is built for the case a paid QA platform is too much for: one test, one script or one agent that needs a real inbox now, with nothing to sign, store or renew.

• Free, with no clock. Mailosaur has no free plan — a 14-day trial, then $20 a month billed annually. GrabMail has no plan to be on: the public domains, the API, your own domain and the MCP server cost nothing and stay that way.
• No key, so no secret and no account. Mailosaur’s API key travels as an HTTP Basic username on every call. GrabMail’s call has no header at all, which is what lets a fork’s pipeline, a public example and an unattended agent use it.
• Your own domain, free. At Mailosaur an inbound custom domain is an Enterprise feature with a custom price. Here it is one MX record at smtp.grabmail.io, and every address on the domain is a catch-all inbox from the first message — the fix for sign-up forms that refuse public disposable domains.
• An MCP server for agents. Mailosaur has none. GrabMail’s at https://grabmail.io/mcp gives an agent an inbox and a blocking wait_for_message of up to 25 seconds, with no OAuth and no sign-up.

Price, side by side

Mailosaur’s prices are “from” figures per month billed annually, in US dollars excluding VAT, with add-ons for SMS and previews. GrabMail’s only paid plan buys access to a pool of domains kept off the disposable-mail blocklists; everything in the table above stays free.

Prices as published on 2 September 2026, excluding VAT. Mailosaur publishes no refund policy; upgrades are prorated and downgrades apply at the next cycle. GrabMail’s pricing page has the full grid.

For developers: reading a mailbox

The whole difference in one command. This reads a GrabMail mailbox with no header, no key and no account:

$ curl -sG https://grabmail.io/api/v1/mailbox --data-urlencode "address=anything@grabmail.io" | jq '{count, alias}'

The Mailosaur equivalent is mailosaur.messages.get(serverId, {sentTo}) in one of eight client libraries, which waits for the message to arrive — a genuinely nicer line to write in a test, paid for with an account, a key and a plan. On GrabMail the wait is a loop with a deadline, shown in the Cypress and Playwright guides, and the OTP guide covers extracting the code once it lands.

The address conventions are close. Mailosaur’s anything@INBOX_ID.mailosaur.net and GrabMail’s anything@grabmail.io both mean “invent a name per test and never create it”. A suite that builds addresses from a run id moves without changing that habit.

For AI agents

Mailosaur does not run an MCP server; its documentation has an llms.txt, which helps a model read the docs but does not give an agent an inbox. GrabMail’s server at https://grabmail.io/mcp does exactly that: create_inbox, a blocking wait_for_message of up to 25 seconds, read_message, with no key and no OAuth.

An agent that signs itself up somewhere needs the keyless version, because getting through a sign-up is the step it cannot do alone. An agent that works inside a QA team’s Mailosaur account can call the REST API with the team’s key like any script. Email for AI agents covers both patterns.

Switching from Mailosaur

A suite that uses Mailosaur for inbound email only moves in an afternoon; one that uses SMS, previews or IMAP should stay. The steps:

1. Change the address builder. name@INBOX_ID.mailosaur.net becomes name@grabmail.io, or name@your-domain.com once its MX record points at smtp.grabmail.io. Nothing to create in either case.
2. Replace messages.get with a wait loop. A GET on /api/v1/mailbox every second until count is above zero or the deadline passes. The guides have it in TypeScript and Python.
3. Remove the key and the library. Delete MAILOSAUR_API_KEY from CI and the client from the lockfile; there is no GrabMail package to add.
4. Check what you relied on. Attachments work here (5 MB per message). Sending, SMS, TOTP, previews, IMAP and per-inbox privacy do not exist here, and mail is gone after 5 days.

Which one, for what

The honest split is by what else the suite has to test:

When to stay with Mailosaur

Three situations where switching would cost you something real:

• Your tests carry real data. Every GrabMail mailbox is readable by anyone who knows the address, on the public domains and on yours. Mailosaur’s inboxes are private. A test that sends a customer’s details needs the second.
• Email is one of several channels. If the same suite verifies SMS codes or TOTP, or checks how a template renders on real devices, Mailosaur does the whole job and GrabMail does a fifth of it.
• You need the long retention or the certificate. Mail here is gone after 5 days and there is no ISO 27001 to attach to a vendor form. If either is on your checklist, stay.

Questions