Checking your email deliverability means verifying that mailbox providers can authenticate your mail, trust your sending domain and IP, and route your messages to the inbox instead of spam or a rejection. You do not need a paid suite to get a clear picture. Run the checks in the order a deliverability engineer would: authentication first, then blocklist status, then live inbox placement, then reputation dashboards, then content and spam scoring.
Reads public DNS only. Nothing is stored unless you save the domain to an account.
The sequence matters. Fixing authentication before you chase a spam-folder problem saves hours, because broken SPF, DKIM or DMARC is the single most common reason good mail lands in spam or gets bounced with a 550 5.7.26 error. Work top down and each step narrows the cause.
Step 1: Audit your authentication (start here)
Authentication is the foundation and the fastest thing to check, so run it first. Paste your domain into the scanner above and it reports SPF, DKIM, DMARC, BIMI, MTA-STS, TLS-RPT, DNSSEC and MX records with a letter grade and specific fixes. This is faster than reading raw DNS by hand and it catches the errors that quietly sink deliverability.
Three things have to be true:
- SPF publishes the IPs and hosts allowed to send for your domain, and it must resolve in ten or fewer DNS lookups per RFC 7208. A record that exceeds that limit throws a PermError and SPF fails entirely.
- DKIM signs each message with a private key so the receiver can verify it against your public key in DNS. A typical selector record looks like
selector1._domainkey.example.com. - DMARC ties SPF and DKIM together with alignment and tells receivers what to do on failure. A minimum policy record reads
v=DMARC1; p=none; rua=mailto:dmarc@example.com.
The subtle failure to watch for is alignment. A message can pass SPF and still fail DMARC if the domain in the visible From header does not align with the SPF or DKIM domain. If your grade looks worse than your raw records suggest, alignment is usually why. Our deeper explainer on SPF, DKIM and DMARC walks through how the three combine, and if you have no DMARC record yet, start with how to set up DMARC.
Do not move to inbox testing until this step is green. There is no point running a seed test against mail that will not authenticate.
Step 2: Check your blocklist and IP reputation
Once authentication is clean, confirm you are not on a blocklist. DNS blocklists (DNSBLs) like Spamhaus, Barracuda and SpamCop are queried by receivers in real time, and a listing can cause outright rejection or aggressive spam filing regardless of how good your records are.
Check both your sending IP addresses and your domain. If you send through a shared pool at an ESP, a neighbor's bad behavior can affect you, which is one reason dedicated IPs matter at volume. Our guide on how to check if your domain is blacklisted covers which lists matter and how to request delisting.
Distinguish IP reputation from domain reputation. A clean IP with a poisoned domain still gets filtered, because Gmail and others weight the sending domain heavily. If you are unclear on the split, read domain reputation vs IP reputation.
Step 3: Run a seed and inbox-placement test
Now measure where mail actually lands. A seed test sends a single campaign to a spread of test addresses across Gmail, Outlook, Yahoo, Apple Mail and common corporate filters, then reports the percentage that hit inbox, spam or vanished.
You can approximate this for free:
- Create your own seed list of real accounts you control across Gmail, Outlook.com, Yahoo and one corporate domain.
- Send the exact campaign you plan to mail, from the same platform and IP, not a stripped-down test.
- Record where each copy lands, and check the message headers on the ones that reach the inbox.
The key is realism. Test the real creative, real links and real from-address, because filters score all of it. A test from a clean internal relay tells you nothing about your production path. Note that provider-specific placement varies, so a Gmail inbox hit does not guarantee an Outlook inbox hit.
Read the Authentication-Results header
On every seeded message, open the raw headers and find the Authentication-Results line. It shows the receiver's own verdict for SPF, DKIM and DMARC, which is the ground truth that overrides whatever a checker predicts. Our walkthrough on how to read the Authentication-Results header shows exactly what pass, fail and none mean in context.
Step 4: Read your Postmaster and reputation dashboards
Seed tests are a snapshot. Provider reputation dashboards are the trend line, and they are free.
- Google Postmaster Tools shows domain and IP reputation, spam-complaint rate, authentication pass rates and delivery errors for mail to Gmail. It is the single most useful free signal for most senders. Set it up following how to set up Google Postmaster Tools.
- Microsoft SNDS (Smart Network Data Services) reports complaint and trap data for your IPs sending to Outlook and Hotmail. Pair it with Microsoft's JMRP feedback loop so you see complaints.
Watch the spam-complaint rate above all else. Google and Yahoo both require senders to stay under 0.3 percent, and a spike there predicts a deliverability collapse before your open rates show it. If you are catching up on the 2024 sender rules, review the Google and Yahoo sender requirements.
Step 5: Test content and spam score
Last, score the message itself. Even authenticated mail from a clean domain gets filtered when the content trips heuristics. Free spam-scoring tools run your email through SpamAssassin-style rules and flag problems:
- Broken or missing List-Unsubscribe header (now required by Gmail and Yahoo for bulk senders).
- Image-heavy mail with little text, or a single large image with no alt text.
- Link domains that differ from your sending domain, or shortened and redirected links.
- Spam-trigger phrasing and ALL-CAPS subject lines.
Content is the last mile. If steps one through four are clean and you still land in spam, the message body and its links are the likely cause. For a broader treatment of filtering causes, see why emails go to spam.
Turn the audit into a repeatable checklist
Run this every quarter and after any change to your sending setup:
- Scan the domain and confirm an A grade on SPF, DKIM, DMARC and alignment.
- Check the sending IP and domain against major blocklists.
- Seed a real campaign across four providers and read the headers.
- Review Postmaster Tools and SNDS for reputation and complaint trends.
- Spam-score the creative before every large send.
If any step regresses, stop and fix it before the next send rather than pushing volume through a broken path. Deliverability problems compound, and a bad send teaches the filters the wrong lesson about your domain.
Frequently asked questions
How do I test email deliverability for free?
Start with the authentication scanner above to confirm SPF, DKIM and DMARC pass, then check blocklists, seed a real campaign to accounts you own across Gmail, Outlook and Yahoo, and review Google Postmaster Tools and Microsoft SNDS. All five steps cost nothing and together give you a full inbox-placement picture.
What is the difference between a deliverability test and an inbox-placement test?
A deliverability test broadly checks whether mail can be delivered at all, covering authentication and blocklist status. An inbox-placement test measures the finer question of whether delivered mail lands in the inbox versus the spam folder at each provider. You need both, and authentication should always be verified first.
Why does my email pass authentication but still go to spam?
Authentication only proves the mail is genuinely from you. Placement also depends on your domain and IP reputation, complaint rates and the content itself. A clean SPF, DKIM and DMARC result with a poor sender reputation or spammy content will still be filtered, which is why the audit runs reputation and content checks after authentication.
How often should I run a deliverability audit?
Run the full five-step audit quarterly and after any infrastructure change, such as switching ESP, adding a sending IP or changing your from-domain. Check Postmaster Tools and your complaint rate weekly if you send in volume, because reputation shifts faster than a quarterly cycle can catch.