MailerLite
mailerlite.com
Sends a newsletter to a small list on a free tier that does not expire
Free tier
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mail-tester.com
Send one email to the address it gives you and get a spam score out of ten.
It generates a throwaway address, you send your newsletter or transactional email to it from the system you actually use, and it returns a SpamAssassin score with each deduction itemised — a broken DKIM signature, a missing unsubscribe header, an image-to-text ratio that looks like a scam. Fixing the itemised list is a genuinely effective hour's work. Results stay available for a week.
AltFTool does this too
If you would rather not leave the site, Email Deliverability Predictor covers the same job here — free, no account, and it runs in your browser.
Open Email Deliverability PredictorQuestions
A genuinely usable free tier with paid plans for volume or team features. Three tests per 24 hours from one address, and the score grades your configuration rather than predicting real inbox placement.
Yes. Mail-Tester 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.
Three tests per 24 hours from one address, and the score grades your configuration rather than predicting real inbox placement.
Alternatives
Same category or same task, ordered by how closely they overlap.
mailerlite.com
Sends a newsletter to a small list on a free tier that does not expire
mailinator.com
Any address at mailinator.com already has an inbox you can read without signing up
mailtrap.io
Catches the emails your app sends in a fake inbox so no real person gets them
zerobounce.net
Checks a mailing list for dead, catch-all and spam-trap addresses before you send
formspree.io
Gives a static site's contact form somewhere to POST that emails you the answers
mxtoolbox.com
Looks up MX, SPF, DKIM and DMARC records and names the one that is wrong