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dmarc poc

DMARC aggregate report viewer (proof of concept)

schlittermann.de
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clear
records
4
parse errors
1
unique source IPs
1
report date range
2026-08-06 — 2026-08-28 02:00:00

Top 10 source IPs

networkcount
MSFT 7

Top 10 header-from domains

domaincount
weasel.example.com 7

Phase 1 — Discovery: who is sending mail from your domains? ⓘYou have published p=none and are collecting data. Nobody is being blocked yet.

Focus on message volume, not IP count — a source sending 50 000 messages is urgent; one sending 3 is noise.

Both-fail sources (DKIM fail AND SPF fail) are either spoofing attempts or services that were set up without telling you. Surface these first.

Expand a domain, then open "By source IP" to see the quadrant breakdown per prefix group.

Sender landscape
both pass SPF fail DKIM fail both fail
weasel.example.com 7
100%
MSFT total 7
IP PTR Total DMARC failures share
2603:10a6:20b:21b::23 — 7
Enterprise Outlook total 7

Top 10 failing source IPs

countsource IPPTR
7 2603:10a6:20b:21b::23ⓘ
domaindispdkimspf#
weasel.example.comrejectfailfail7
 		—
source IPheader-fromcount dispositionDKIMSPFreport begin
2603:10a6:20b:21b::23 weasel.example.com 2 reject fail fail 2026-08-06 02:00
2603:10a6:20b:21b::23 weasel.example.com 2 reject fail fail 2026-08-20 02:00
2603:10a6:20b:21b::23 weasel.example.com 2 reject fail fail 2026-08-24 02:00
2603:10a6:20b:21b::23 weasel.example.com 1 reject fail fail 2026-08-28 02:00

Phase 2 — Hardening: what would break if you tightened the policy? ⓘYou understand your sender landscape and want to move from p=none toward p=quarantine or p=reject. The risk is collateral damage to legitimate mail.

Policy readiness % = share of messages that would survive a reject policy today.

SPF-only sources need DKIM signing added in their sending platform.

DKIM-only sources need their SPF record aligned with your From: domain.

No DMARC alignment sources send all mail failing — configure or block.

Inconsistent sources have mixed results — investigate per-IP.

DMARC readiness
both pass SPF fail DKIM fail both fail
weasel.example.com 7 / 7
100%
MSFT 7 / 7
IP PTR Fail / Total DMARC failures share
2603:10a6:20b:21b::23 — 7 / 7

no DMARC alignment

Enterprise Outlook total 7

Top 10 failing source IPs

countsource IPPTR
7 2603:10a6:20b:21b::23ⓘ
domaindispdkimspf#
weasel.example.comrejectfailfail7
 —
source IPheader-fromcountdispositionDKIMSPFreport begin
2603:10a6:20b:21b::23weasel.example.com2reject fail fail 2026-08-06 02:00
2603:10a6:20b:21b::23weasel.example.com2reject fail fail 2026-08-20 02:00
2603:10a6:20b:21b::23weasel.example.com2reject fail fail 2026-08-24 02:00
2603:10a6:20b:21b::23weasel.example.com1reject fail fail 2026-08-28 02:00

Phase 3 — Steady state: did something break? Is anyone spoofing you? ⓘYou have a tight policy in place (p=quarantine or p=reject). Watch for anomalies.

New sources — an IP appearing for the first time in the last 30 days that was not seen before. Could be a new legitimate sender nobody configured, or the start of a spoofing campaign.

Active failures — sources still failing DMARC under a strict policy in the last 30 days. Persistent failures with high volume are either spoofing or a misconfigured legitimate service that needs fixing.

If a major reporter (Google, Microsoft) stops appearing, your rua= address may be bouncing.

Alignment health — last 30 days
both pass SPF fail DKIM fail both fail
08-06
08-20
08-24
08-28
weasel.example.com 7 / 7
100%
08-06
08-20
08-24
08-28
MSFT new failing 7 / 7
IP PTR Fail / Total DMARC failures share
2603:10a6:20b:21b::23 — 7 / 7
Enterprise Outlook total 7

Top 10 failing source IPs

countsource IPPTR
7 2603:10a6:20b:21b::23ⓘ
domaindispdkimspf#
weasel.example.comrejectfailfail7
 —
source IPheader-fromcountdispositionDKIMSPFreport begin
2603:10a6:20b:21b::23weasel.example.com2reject fail fail 2026-08-06 02:00
2603:10a6:20b:21b::23weasel.example.com2reject fail fail 2026-08-20 02:00
2603:10a6:20b:21b::23weasel.example.com2reject fail fail 2026-08-24 02:00
2603:10a6:20b:21b::23weasel.example.com1reject fail fail 2026-08-28 02:00