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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mailtrap.io
Catches the emails your app sends in a fake inbox so no real person gets them.
Point your staging environment's SMTP settings at Mailtrap and every message your application sends lands in a sandbox inbox instead of a customer's. You get the rendered HTML, the text alternative, the raw source, a spam analysis and an HTML-support check per client, which is where broken layouts show up. It removes the classic accident of a test run emailing your production list.
Questions
A genuinely usable free tier with paid plans for volume or team features. The free sandbox is one inbox with a small monthly cap on captured messages, and actually sending mail is a separate paid product.
Yes. Mailtrap Email Testing 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.
The free sandbox is one inbox with a small monthly cap on captured messages, and actually sending mail is a separate paid product.
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
mailinator.com
Any address at mailinator.com already has an inbox you can read without signing up
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