Fourteen tools. Every signal behind the inbox.
Each instrument isolates one thing mailbox providers check: authentication, blocklists, DNS, infrastructure or content. Run them in any order, or start with the full reputation grade and let it point you to the rest.
Reputation & analysis
Sender Reputation Checker
One A to F grade across authentication, blacklists, DNS and infrastructure, plus the fixes that matter most.
Grade a domainBlacklist Checker
Check a domain’s mail servers or any IP against 15+ public DNS blocklists in one pass.
Scan blocklistsEmail Header Analyzer
Paste raw headers to trace every hop, measure delays and read SPF, DKIM and DMARC verdicts.
Analyze headersDMARC Report Analyzer
Upload the XML aggregate reports mailbox providers send and see which sources pass and fail, parsed in your browser.
Analyze reportsEmail Spam Checker
Paste a subject and body to score the content signals that trip spam filters, before you send.
Check contentAuthentication
SPF Record Checker
Parse every mechanism and count DNS lookups against the hard limit of 10.
Check SPFDKIM Record Checker
Find published DKIM keys across common selectors and measure their key length.
Check DKIMDMARC Record Checker
Read your policy, alignment mode, percentage and reporting addresses.
Check DMARCBIMI Record Checker
Verify your BIMI record, the logo it points to and the DMARC enforcement it depends on.
Check BIMIRecord generators
SPF Record Generator
Pick your sending services and build a valid SPF record with a live lookup count.
Build SPFDMARC Record Generator
Generate a _dmarc record with the right policy and reporting for a safe rollout.
Build DMARCDKIM Key Generator
Generate a 2048-bit DKIM key pair in your browser and the DNS record to publish for it.
Generate keysWhich tool for which symptom
| You see | Open |
|---|---|
| Mail lands in spam, no clear reason | Reputation Checker |
| Bounce mentions a blocklist | Blacklist Checker |
| SPF permerror or softfail | SPF Checker |
| dkim=fail or no signature | DKIM Checker |
| Gmail 5.7.26 or DMARC fail | DMARC Checker |
| 5.7.25 or "no PTR" rejections | Reverse DNS |
| One message arrived late or oddly | Header Analyzer |
| DMARC reports piling up unread | DMARC Report Analyzer |
| A campaign might trip content filters | Spam Checker |
| Your logo does not show in Gmail | BIMI Checker |
| You run your own mail server and need a DKIM key | DKIM Key Generator |
What a healthy domain looks like
Across every check, the same baseline shows up. One valid SPF record under ten lookups. A 2048-bit DKIM key signing with your own domain. A DMARC policy at quarantine or reject with reports flowing. MX and PTR records that resolve cleanly, and no blocklist listings.
Get there and the technical side is done. What remains is behaviour: sending wanted mail to clean lists, which no DNS record can fake. Our deliverability guide covers that half.
Common questions about the tools
Are these email deliverability tools really free?
Yes. Every tool is free with no signup, no email address and no usage cap for normal use. They read public DNS and blocklist data, which anyone can query, so there is nothing to sell you access to.
Which tool should I run first?
Start with the Sender Reputation Checker. It runs every other check in one pass, grades each category, and tells you which dedicated tool to open next.
Do you store the domains I check?
No. Lookups run in your browser through public DNS-over-HTTPS resolvers (Cloudflare, with Google as a fallback). Nothing you type is sent to or logged by our servers.
How often should I check my setup?
Monthly if you send regularly, weekly at high volume, and immediately after any DNS change, ESP migration, or a sudden drop in opens or rise in bounces.
What do Google, Yahoo and Microsoft require from bulk senders?
Anyone sending around 5,000 or more messages a day to their users needs SPF, DKIM and DMARC (at least p=none) with alignment, a one-click unsubscribe, valid forward and reverse DNS, TLS, and a spam complaint rate kept under 0.3% (ideally under 0.1%).
Can these tools see my spam complaint rate?
No. Complaint and engagement data is private to each mailbox provider. Pair these checks with Google Postmaster Tools and Microsoft SNDS, which show the reputation Gmail and Outlook actually assign you.
Check your domain before you hit send.
Run the full check: SPF, DKIM, DMARC, 15+ blocklists, MX, reverse DNS and infrastructure, scored A to F with a ranked list of fixes.