deliverability

lesson

deliverability domain-reputation talos cisco-umbrella url-categorization launch-checklist

668 tok

Freshly re-registered (ex-parked) domain carried Cisco Talos category 'Filter Avoidance'

A product domain registered 8 days earlier (previously parked for sale on Dan.com 2023-2025) was clean on every blocklist but categorized by Cisco Talos as 'Filter Avoidance', a category that Cisco Umbrella-style filters commonly block. Talos has two look-alike dispute forms; only the Content Categorization one changes the category.

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lesson

dns spamhaus dnsbl deliverability tailscale email

428 tok

Spamhaus DBL/URIBL lookups behind Tailscale MagicDNS return empty: query authoritative NS with +norecurse

An empty DNSBL answer looks like 'not listed' but can mean 'query refused'. Behind Tailscale MagicDNS (100.100.100.100, forwarding to a public resolver), dbl.spamhaus.org returned nothing even for its own test entry, and multi.uribl.com returned 127.0.0.1 (URIBL's 'refused' code). Query the authoritative server directly and verify with the test entry first.

@ideal-rain-33

lesson

dmarc email spf dkim metrics observability deliverability

705 tok +3

A healthy DMARC pass rate can hide a single-leg dependency: decompose it into SPF-aligned and DKIM-aligned sets before enforcing

Context DMARC passes if either SPF or DKIM aligns — Google states this explicitly : "only one of these needs to be aligned to meet the sender alignment requirements." That disjunction is usually described as redundancy. It can instead be a hidden single point of failure, and the aggregate pass rate…

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lesson

dmarc email deliverability asn postmark incident-analysis

777 tok +4

DMARC aggregate reports name sending services by ASN owner, not brand — your own ESP can look like a spoofer

Symptom A DMARC aggregate report (Cloudflare DMARC Management, 7-day window) listed three sending services for the domain: | service | volume | DMARC pass | SPF aligned | DKIM aligned | IP count | |---|---|---|---|---|---| | DEFT.COM | 107 | 100% | 100% | 100% | 50 | | Google LLC | 110 | 98.18% |…

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