Conciseness

The body is dense and imperative ("Get email into inboxes, not spam folders. Set up authentication. Monitor reputation."), but includes a few explanations Claude already knows, e.g. the full acronym expansion "Domain-based Message Authentication, Reporting, and Conformance" and "DKIM proves the message wasn't modified in transit and that the sender controls the domain". Anchor 4 fits: efficient with minor instances of over-explanation that could be trimmed; not 5 since not every token earns its place.

Actionability

Fully executable guidance throughout: copy-paste dig commands ("dig +short txt _dmarc.example.com"), complete TXT record templates, exact thresholds ("target: under 2%", "under 0.1%"), a concrete rollout schedule ("pct=10", "start at 50/day, 2x daily"), and named tools (Google Postmaster Tools, dmarcian, mail-tester). Matches anchor 5's copy-paste-ready commands covering the common cases; no meaningful execution gaps for an instruction-only skill.

Workflow Clarity

A clear 8-step sequence where the risky core (DMARC) has explicit validation ("Verify lookup count is under 10", "check headers for dkim=pass", "Watch reports for at least 2-4 weeks") and a monitor→fix→escalate feedback loop. Anchor 4 fits rather than 5 because steps 4-6 (list hygiene, content audit, growth) lack verification checkpoints, e.g. no re-check of complaint rate after hygiene fixes or before/after content test.

Progressive Disclosure

Good structure with one clearly signaled, one-level-deep reference (references/dmarc-rollout-playbook.md, verified to exist, with a description of its contents) that keeps the deep DMARC rollout detail out of the overview. Anchor 4 rather than 5 because the ~275-line body still inlines content that could be split (BIMI requirements, and Step 2's DMARC fix order that overlaps the playbook's scope), and a multi-pillar domain is served by only one reference file.

Specificity

Lists five concrete actions with named protocols ("setting up email authentication (SPF, DKIM, DMARC)", "diagnosing emails landing in spam", "monitoring sender reputation", "hardening against email spoofing"), with minor gaps such as list hygiene and bounce handling absent from the action list. Not a 5 because coverage of the domain's actions is not fully comprehensive; well above anchor 3's 1-2 actions.

Completeness

Explicitly answers both what ("Make sure email actually reaches inboxes" plus the enumerated actions) and when ("Use this skill when...", "Triggers on...", "Also triggers when...") with concrete trigger phrases. Exact match to anchor 5; anchor 4's 'when could be more explicit' does not apply.

Trigger Term Quality

"Triggers on email deliverability, SPF, DKIM, DMARC, spam folder, sender reputation, mailbox provider, soft bounces, bounce rate, BIMI, MTA-STS, deliverability audit" plus "when a marketing or transactional email isn't reaching users" covers natural phrasing and synonyms ("spam folder" / "landing in spam" / "isn't reaching users"). Matches anchor 5's comprehensive coverage including synonyms; no common variant is missing.

Distinctiveness Conflict Risk

The niche is unambiguous — domain-specific protocol acronyms (SPF, DKIM, DMARC, BIMI, MTA-STS) are trigger terms that only apply to email deliverability, giving minimal conflict risk with other skills. Matches anchor 5; not anchor 4 since no closely related skill would plausibly capture these triggers.