Spare Mailbox

Most temporary email services will not tell you how long they keep your mail. A survey of twelve of them in September 2026 found only four published a retention figure; the rest required a test message and a stopwatch to find out.

Spare Mailbox publishes its numbers instead. Messages are kept for 24 hours on a sliding window that extends on every new arrival, with a seven-day hard ceiling, and each inbox holds up to 10 messages or 25 MB. Addresses are permanent, so you can pin one to a test fixture and reuse it rather than regenerating before every run. No account, no password, no registration.

HTML renders in a sandbox and attachments download as inert files, so a hostile message cannot execute in your browser. Full headers and the raw message source are available when you need them.

There is also a developer API for automated testing: plain GET endpoints return an address, its inbox, and a message body, so a Playwright or Cypress suite waiting on a verification email can simply read it. Two headers, no SDK. The free tier is 50 requests a month with no card required.