Paste the raw header. You get the route the message took, where the time went, and whether SPF, DKIM and DMARC lined up — in plain English, with the technical detail folded away.
Email headers usually contain the recipient's address and your internal server names. Nothing you paste here is uploaded or stored — the parsing runs in your browser, on your machine, and the header never reaches us.
Everything from the top of the raw message down to the first blank line. Pasting the whole raw message works too — only the header part is read.
Every email carries a header — a block of technical lines your mail app hides by default. It records which servers handled the message, when each one took it, whether the sender was authenticated, and which addresses were used behind the visible From line. It is the closest thing email has to a delivery receipt, and it is the first place to look when a send arrives late, arrives wrong, or doesn't arrive at all.
You don't need to read the whole block. Four things carry almost all of the useful information.
Each server that handles a message adds its own Received line above the ones already there, so the oldest hop sits at the bottom of the header and the last one sits at the top. Read from the bottom up and you are following the message in the order it actually travelled. It is the single most common thing people get backwards, and getting it backwards makes every timestamp on the page read wrong.
Every Received line carries the timestamp of the moment that server accepted the message, so the difference between one line and the next is the wait at that step. Most handovers take under a second. A gap of several minutes almost always means the receiving server deliberately made your sender wait — greylisting an unfamiliar sender, or holding the message in a queue — and that is a reputation signal, not a technical error.
The receiving server writes down what it made of your sender identity, usually in one line near the top. SPF says whether the sending server was allowed to use that domain. DKIM says whether the message arrived unaltered. DMARC says whether either of those passed for the domain your readers actually see — which is exactly why DMARC can fail while SPF and DKIM both pass.
The From line is what your readers see. The Return-Path is where bounces go, and when you send through a platform it usually belongs to the platform rather than to you. That mismatch is normal on its own. It turns into a deliverability problem when your From domain is not authenticated for that platform, because then nothing aligns and DMARC fails — the most common authentication failure in newsletter sending.
Open the email you want to look at, then:
Open the message, click the three dots at its top right, and choose Show original. A new tab opens with the full raw message and a Copy to clipboard button.
In the desktop app, open the message in its own window, then File and Properties, and copy the box marked Internet headers. On the web, open the message, click the three dots and look under View — depending on your version it is View message source or message details.
Select the message, then View, Message, Raw Source. All Headers gives you a shorter version if the raw source is more than you need.
Open the message, click the three dots above it, and choose View raw message.
Everything on this page is backward-looking. A header describes a message that already arrived, in one mailbox, and it describes it well — the route, the delay, the authentication, the addresses. What it cannot do is tell you where your next newsletter will be filed. Inbox placement depends on how each provider weighs your reputation and on how your subscribers behave, and none of that is written into a header. A spam score has the same limit, for the same reason.
When SPF and DKIM pass but DMARC fails, the answer is nearly always the same: your From domain is not authenticated for the platform you send through, so authentication is passing for the platform's domain instead of yours. Every platform has a setup for this and each one calls it something slightly different. Here is the walkthrough for the common ones.
So you don't reach for the wrong tool: everything here is about whether your mail reaches the inbox. Whether an email address actually exists and can receive mail is a different job, and that is what verifiers like ZeroBounce and NeverBounce do. A clean list of valid addresses can still land in spam, and a perfectly authenticated email can still be sent to addresses that stopped working years ago. If your question is "will this reach the inbox", you're in the right place; if it's "are these addresses real", you want a verifier.
A header told you what happened to one message. The question that actually costs you money is where the next one goes. Forward your email to the address below and in about 30 seconds you get the split across real Gmail, Outlook and Yahoo accounts — Primary, Promotions or Spam — a plain-English verdict, and the three fixes worth doing first. Free, no signup. Made in Slovakia, EU-hosted, GDPR by default, and hello@mailtester.ai is answered by a real person.
Forward your email → see where it landsPaste the raw header. You get the route the message took, where the time went, and whether SPF, DKIM and DMARC lined up — in plain English, with the technical detail folded away.
If you've ever searched "email tester," half the results check whether the address is valid. We do the other thing — whether the email itself will reach the inbox once you press send.
You upload a CSV of subscribers. The tool tells you which addresses bounce. Great for cleaning a stale list before a re-engagement send.
You forward one email — newsletter, launch, client note — to a one-time mailbox. We open it in real Gmail, Outlook, and Yahoo and tell you which tab it landed in, plus what to rewrite before you send it to your list.
Paste the mailbox above into the test-send field in Beehiiv, Kit, Substack, Mailchimp — or your own inbox. Hit go. We never see your subscriber list.
In real Gmail, real Outlook, real Yahoo. We watch where your email lands — Primary, Promotions, or Spam — using the same filters that decide whether your campaign worked.
Plain English. Three things to change, in priority order. Unlock the bundle and we generate a subject, body, and CTA rewrite in your voice — paste them back into your campaign before lunch.
Forward any email and get the score — free and unlimited. Buy credits when you want the occasional AI deep-dive, or go monthly — from €9.99 — if you send regularly. Cancel from the same screen you upgrade on.
Takes less time than picking a hero photo. No card, no signup, no anything.