Is Mailsac a free alternative to Mailisk?

Both have a free plan, measured differently. Mailisk’s gives you 500 received emails a month in one random namespace, kept for 1 day, and the namespace expires after a month. Mailsac’s gives you an API key, one private address and 1,500 Ops a month with no expiry, plus public @mailsac.com inboxes that need no account at all and are not counted when mail arrives. At 3 to 6 Ops per polled test, the free Mailsac plan covers roughly 250 to 500 test runs a month on private addresses, and far more if the address pushes to a webhook.

What is the Mailsac equivalent of a Mailisk namespace?

A custom domain. On Indie and up, a yourteam.msdc.co subdomain is ready immediately with no DNS work, every address on it exists without setup, and only your account and team can read it, which is what a Mailisk namespace gives you. Unlike Mailisk, you can also verify your own domain with a TXT record and MX records, so test addresses look like signup-123@qa.yourcompany.com. Indie includes one domain, Business five and Business+ ten; extra domains are $7 a month. If you only need one fixed private address, the free plan includes it.

Mailisk’s API waits for the email. Does Mailsac’s?

Not on the server. Mailisk’s wait flag holds the request open until a matching email exists, and its clients do that by default with a 5-minute timeout. On Mailsac you either poll GET /api/addresses/{email}/messages in a short loop with a deadline, as in the snippet above and the playwright-signup-ci example, or let Mailsac push: a private address or custom domain can forward every message to a webhook or WebSocket on every plan, so the test waits on one connection and uses one Op per email. In Cypress, cy.mailsacWaitForMessage() from @mailsac/cypress does the waiting for you.

How do Mailsac Ops compare with Mailisk’s received emails?

They measure different things, so there is no exact conversion. Mailisk counts emails received a month, with separate allowances for sent emails and SMS, and limits API calls to 3,600 an hour per key rather than counting them. Mailsac counts Ops: each message received at a private address or domain, each API call, and each webhook, Slack or WebSocket push. A test that polls for one email and reads it typically uses 3 to 6 Ops, and a pushed email uses 1, so Indie’s 25,000 Ops cover several thousand tests a month and Business’s 500,000 cover roughly 150,000 test emails. Mail to public @mailsac.com inboxes is not counted at all.

Does Mailsac test SMS or TOTP codes?

No. Mailsac receives email and hands it to your tests over the API, webhooks or WebSockets. Mailisk includes one US, UK or Canadian SMS number on tiers from $29 a month, reads inbound texts through the same kind of search call, and generates TOTP codes from a shared secret or a saved virtual authenticator device. If SMS or authenticator-app MFA is part of your suite, Mailisk is the better fit.

How long is test mail kept?

Mailisk keeps each email for a fixed time: 1 day on the free plan and 3, 10 or 15 days on paid tiers, with longer retention on request; attachments are deleted with the email, and there is no delete call, so cleanup is automatic. Mailsac keeps private mail up to your plan’s stored-message count (1,000 on Indie, 5,000 on Business, 10,000 on Business+), recycling the oldest first and keeping anything you star, and you can delete a message, an inbox or a whole domain’s mail on demand. Public @mailsac.com mail is kept up to 4 days, and only the most recent few messages per inbox.

Is Mailsac a drop-in replacement for the Mailisk API?

No. The endpoints, the auth header and the message JSON are different, and Mailsac has no server-side wait, so the code that finds and reads the email needs rewriting. The mapping above covers every inbound-email call in Mailisk’s API reference. Your app and its email sending do not change; only the recipient domain and the code that reads the mail. Tests that depend on Mailisk’s SMS, TOTP or outbound sending have no Mailsac equivalent.