Mail-Tester
mail-tester.com
Send one email to the address it gives you and get a spam score out of ten
Free tier
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mailinator.com
Any address at mailinator.com already has an inbox you can read without signing up.
Invent an address on the spot, use it in a signup form, then type the same name on the site to read what arrived — no registration, no password, no setup step. It is the fastest way through a verification email for a service you have no intention of keeping. It has worked this way since 2003 and is the reason 'disposable email' became a category.
Questions
A genuinely usable free tier with paid plans for volume or team features. Public inboxes are readable by anyone who guesses the name and messages are purged within hours; private domains, the API and SMS testing are paid.
Yes. Mailinator sends your input to its own servers to process it. That is fine for public material; for anything containing personal data, use one of the on-device tools instead.
Public inboxes are readable by anyone who guesses the name and messages are purged within hours; private domains, the API and SMS testing are paid.
Alternatives
Same category or same task, ordered by how closely they overlap.
mail-tester.com
Send one email to the address it gives you and get a spam score out of ten
mailtrap.io
Catches the emails your app sends in a fake inbox so no real person gets them
formspree.io
Gives a static site's contact form somewhere to POST that emails you the answers
mailerlite.com
Sends a newsletter to a small list on a free tier that does not expire
mxtoolbox.com
Looks up MX, SPF, DKIM and DMARC records and names the one that is wrong
proton.me
Encrypted mailbox where the provider cannot read the contents of your messages