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dmarc poc

DMARC aggregate report viewer (proof of concept)

schlittermann.de
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clear
records
5
parse errors
1
unique source IPs
1
report date range
2026-05-18 — 2026-08-25 02:00:00

Top 10 source IPs

networkcount
MSFT 8

Top 10 header-from domains

domaincount
weasel.example.com 4
yak.example.com 4

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 4
100%
MSFT total 4
IP PTR Total DMARC failures share
2603:10a6:10:28c::22 — 4
Enterprise Outlook total 4

Top 10 failing source IPs

countsource IPPTR
4 2603:10a6:10:28c::22ⓘ
domaindispdkimspf#
weasel.example.comrejectfailfail4
 		—
source IPheader-fromcount dispositionDKIMSPFreport begin
2603:10a6:10:28c::22 weasel.example.com 1 reject fail fail 2026-07-26 02:00
2603:10a6:10:28c::22 weasel.example.com 1 reject fail fail 2026-08-18 02:00
2603:10a6:10:28c::22 weasel.example.com 1 reject fail fail 2026-08-20 02:00
2603:10a6:10:28c::22 weasel.example.com 1 reject fail fail 2026-08-25 02:00
yak.example.com 4
100%
MSFT total 4
IP PTR Total DMARC failures share
2603:10a6:10:28c::22 — 4
Enterprise Outlook total 4

Top 10 failing source IPs

countsource IPPTR
4 2603:10a6:10:28c::22ⓘ
domaindispdkimspf#
yak.example.comrejectfailfail4
 		—
source IPheader-fromcount dispositionDKIMSPFreport begin
2603:10a6:10:28c::22 yak.example.com 4 reject fail fail 2026-05-18 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 4 / 4
100%
MSFT 4 / 4
IP PTR Fail / Total DMARC failures share
2603:10a6:10:28c::22 — 4 / 4

no DMARC alignment

Enterprise Outlook total 4

Top 10 failing source IPs

countsource IPPTR
4 2603:10a6:10:28c::22ⓘ
domaindispdkimspf#
weasel.example.comrejectfailfail4
 —
source IPheader-fromcountdispositionDKIMSPFreport begin
2603:10a6:10:28c::22weasel.example.com1reject fail fail 2026-07-26 02:00
2603:10a6:10:28c::22weasel.example.com1reject fail fail 2026-08-18 02:00
2603:10a6:10:28c::22weasel.example.com1reject fail fail 2026-08-20 02:00
2603:10a6:10:28c::22weasel.example.com1reject fail fail 2026-08-25 02:00
yak.example.com 4 / 4
100%
MSFT 4 / 4
IP PTR Fail / Total DMARC failures share
2603:10a6:10:28c::22 — 4 / 4

no DMARC alignment

Enterprise Outlook total 4

Top 10 failing source IPs

countsource IPPTR
4 2603:10a6:10:28c::22ⓘ
domaindispdkimspf#
yak.example.comrejectfailfail4
 —
source IPheader-fromcountdispositionDKIMSPFreport begin
2603:10a6:10:28c::22yak.example.com4reject fail fail 2026-05-18 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
05-18
07-26
08-18
08-20
08-25
weasel.example.com 4 / 4
100%
05-18
07-26
08-18
08-20
08-25
MSFT new failing 4 / 4
IP PTR Fail / Total DMARC failures share
2603:10a6:10:28c::22 — 4 / 4
Enterprise Outlook total 4

Top 10 failing source IPs

countsource IPPTR
4 2603:10a6:10:28c::22ⓘ
domaindispdkimspf#
weasel.example.comrejectfailfail4
 —
source IPheader-fromcountdispositionDKIMSPFreport begin
2603:10a6:10:28c::22weasel.example.com1reject fail fail 2026-07-26 02:00
2603:10a6:10:28c::22weasel.example.com1reject fail fail 2026-08-18 02:00
2603:10a6:10:28c::22weasel.example.com1reject fail fail 2026-08-20 02:00
2603:10a6:10:28c::22weasel.example.com1reject fail fail 2026-08-25 02:00
yak.example.com 4 / 4
100%
05-18
07-26
08-18
08-20
08-25
MSFT new failing 4 / 4
IP PTR Fail / Total DMARC failures share
2603:10a6:10:28c::22 — 4 / 4
Enterprise Outlook total 4

Top 10 failing source IPs

countsource IPPTR
4 2603:10a6:10:28c::22ⓘ
domaindispdkimspf#
yak.example.comrejectfailfail4
 —
source IPheader-fromcountdispositionDKIMSPFreport begin
2603:10a6:10:28c::22yak.example.com4reject fail fail 2026-05-18 02:00