Inbox Inspector

See what your ESPs really send

Paste a unique mon-…@monitor.dmarctrust.com address into any seed list in Mailchimp, SendGrid, Klaviyo, or 30+ other ESPs. We receive every campaign as a real MTA, evaluate SPF, DKIM, and DMARC ourselves, detect the ESP, and surface the verdicts.

Start free How it works
30 ESPs auto-detected Trusted RFC 8601 evaluation DMARC alignment surfaced No browser test, no plugin

Built by Florian Le Goff & Marc Lelu, ex-Mailjet deliverability engineers. Last updated May 24, 2026.

Your ESP's success metric is "200 OK". Yours is "passed DMARC at the recipient."

Your ESP returns a 200, the campaign hits inboxes, dashboards look green. Yet your DMARC reports later show p=quarantine hits from that exact sender. The most common cause is DKIM signed under the ESP's domain, not yours, with no SPF alignment to compensate. See RFC 7489 §3.1 on DMARC alignment.

Inbox Inspector is the missing feedback loop. We evaluate every campaign you route through the seed address the way a real recipient would, then explain the result.

How it works in 3 steps

1

Enable Inbox Inspector on a domain

One click in the dashboard. You receive a unique mon-…@monitor.dmarctrust.com address.

2

Paste it into your ESP's seed list

Same place you put your own internal QA mailboxes. Every campaign now sends a copy to us.

3

We verify and group by ESP

SPF, DKIM, DMARC, alignment, and disposition, all per-campaign, with a 30-day rollup per ESP.

What every message detail page tells you

  • Verdict timeline. SPF → DKIM → DMARC → alignment → final disposition, in order.
  • By-ESP 30-day scorecard. DMARC pass rate, SPF pass rate, DKIM pass rate, alignment rate.
  • Raw Authentication-Results on demand. Toggle to see exactly what we stamped, with the original headers untouched.
  • Original .eml download. Hand it to your ESP for support, or run it through the free Email Header Analyzer.

We don't tell you which Gmail tab. We tell you why authentication broke.

Placement testers answer

"Did this campaign land in inbox, promotions, or spam?"

Inbox Inspector answers

"Did SPF align? Did DKIM survive ESP rewriting? Did your DMARC policy fire? What ESP and what IP?"

These two questions are complementary. Most teams want both. Inbox Inspector is the authentication half.

Included in every plan, with monthly quotas

Free

1 msg/mo

Try one campaign per month

Starter

50 msgs/mo

$19/mo, full auth verdicts

Pro

100 msgs/mo

$49/mo, alerts on DMARC fail

When you go over quota we still accept the message as an envelope-only stub, so you see it happen instead of wondering why a campaign disappeared. See pricing

Works alongside

Protect inbound transport with hosted MTA-STS

Enforce TLS on incoming mail with one CNAME. We host the policy.

Read more →

Turn DMARC aggregate reports into a dashboard

Read the daily XML feed without parsing XML.

Read more →

Email Header Analyzer (free tool)

Paste raw headers, get the same authentication verdict.

Read more →

Frequently asked questions

What ESPs do you auto-detect?
Mailchimp, SendGrid, Mailgun, Postmark, Customer.io, Klaviyo, Brevo, Resend, Iterable, Braze, Salesforce Marketing Cloud, and 19 more. The full list is maintained in our open ESP signatures file.
Does this replace DMARC aggregate reports?
No. DMARC aggregate reports are produced by recipient mail providers and describe everything they saw. Inbox Inspector tests one specific campaign you sent through one specific ESP. They are complementary.
Why a unique address per domain?
The address routes incoming mail to your account, and unique tokens prevent third parties from injecting fake test traffic into your dashboard.
What happens if I exceed my monthly quota?
Over-quota messages are still accepted at SMTP and stored as envelope-only stubs (no SPF/DKIM evaluation, headers not retained). The UI shows a clear warning so you know you are over.
Can an ESP forge its own Authentication-Results header to look like a pass?
No. We ignore any Authentication-Results header whose authserv-id is not ours and stamp our own using opendkim and opendmarc in verify-only mode. This follows the trusted-authentication-results pattern in RFC 8601 §5.
How is this billed?
Inbox Inspector is included in your existing DMARCTrust plan with no add-on cost. Free plans get 1 message per month, Starter 50, Pro 100.

Find every authentication gap your ESP isn't telling you about

Paste one address. Start seeing per-campaign DMARC verdicts today.

Start free See pricing