If you've ever tried to debug an email deliverability problem in a hurry, you know this feeling. It's 10 AM. A client pings you: "Our newsletter is going to spam again." You open mail-tester.net, send a test, get a score, tweak the SPF record, send another test. Two tests in, you've already used two-thirds of your free daily quota. You fix the DKIM, run a third test - and now you're locked out until tomorrow unless you pay.
Meanwhile, MXToolbox wants your credit card up front. GlockApps gives you a trial and then a sales call. The free tiers of the "free" tools are honestly just demos.
I hit this wall over and over. Not occasionally - constantly. Running a SaaS in the email space means deliverability isn't a side problem, it's the whole game. Every new client migration, every SMTP reconfig, every new sending domain, every time a transactional email started bouncing - I needed to test. And every tool either gated the good stuff, showed me a 2012-era interface, or rate-limited me into uselessness.
So I built my own. And I made it free. Unlimited. No signup. Because the version of this tool I always wanted to exist didn't.
What a "deliverability test" actually needs to check
A lot of the older tools only scratch the surface. You send an email, they check SPF, DKIM, DMARC, throw a couple of RBLs at you, and give you a number. That's fine for a quick sanity check, but it doesn't tell you why your email went to spam - and it doesn't catch the subtle stuff.
I wanted the tester to actually be useful for real debugging. So here's what it checks on every send:
Authentication layer. SPF record alignment, DKIM signature validation, DMARC policy and alignment. The holy trinity - but checked properly, including alignment mode (relaxed vs. strict), which is where most "but my SPF passes!" confusion comes from.
Spam scoring with Rspamd. This is the piece most free testers skip. Rspamd is what real mail servers use to score incoming mail. If your email scores badly in Rspamd, it's going to score badly at Gmail too. Running it locally on the test inbox catches content issues - bad HTML-to-text ratios, suspicious link patterns, header anomalies - that pure authentication checks miss entirely.
Blacklist check across 23 RBLs. Spamhaus, Barracuda, SORBS, SpamCop, and twenty more. One listing on the wrong RBL and your delivery rate tanks. You need to know immediately, not when your open rate drops next week.
Infrastructure checks. Reverse DNS (PTR) matches, HELO/EHLO hostname, TLS encryption, MX and A record validation. The boring stuff that quietly kills inbox placement.
Header hygiene. List-Unsubscribe, Message-ID format, Return-Path, proper Content-Type. Gmail and Microsoft care about these - a lot - and most testers don't flag when they're missing or malformed.
Twelve check categories, one score, actionable fixes for every failure.
The bits I added because the alternatives didn't have them
Two features I kept wishing existed on other testers:
Shareable public reports. When you're a consultant or an agency running an audit for a client, you don't want to screenshot a dashboard into a PDF. You want to send a link. So every test result has a public URL you can share. The client sees the same report you see - authentication status, blacklist hits, Rspamd breakdown, the whole thing.
Embeddable score badge. If you're selling email deliverability services, or you just want to show off that your sending domain scores 98/100, you can drop a small badge onto your site. It pulls the latest score live. Consultants love this one - it's a trust signal that costs nothing.
Neither of these exist on mail-tester.net or MXToolbox. They're small, but they're the kind of thing that turns a one-off tool into something you actually bookmark and come back to.
Why free, unlimited, no signup
I run SendBridge. This tester sits inside the same product. If you eventually need email verification, list cleaning, or the API - great, that's my business. But I'm not going to cripple the free tool to funnel you into a signup form. That's the move I hated when every other tool did it to me.
The tester is free because deliverability is a foundational problem in this industry, and gating the basic diagnostic feels wrong. If you're a solo founder sending your first transactional email, a consultant running a client audit, or a developer debugging SMTP at 2 AM - you should be able to run as many tests as you need without hitting a paywall or a signup wall.
No account. No credit card. No daily cap. Open the page, get a unique test address, send your email, get your score. That's it.
Who it's for
Developers debugging SPF/DKIM/DMARC on a new sending domain
Email marketers pre-flighting a campaign before blasting 50,000 contacts
Consultants running client deliverability audits with shareable reports
Agencies who want to embed a live score badge on the client dashboard
Anyone who's ever been locked out of mail-tester at 10 AM and thought "there has to be a better way"
Try it: sendbridge.com/mail-tester. No signup. Unlimited. Forever free.
If you find a check that's missing or a bug in the report, tell me. I'm actively building this one out.