Senderkit email deliverability

SenderKit email deliverability

Use this open-source skill to get authenticated, inbox-landing transactional email. It diagnoses a sending domain's authentication, generates the exact DNS records to fix it, and verifies the result — using standard tools (dig/nslookup) that need no install, signup, or API key. The reusable source lives at https://github.com/senderkit/senderkit-skills in the skills/senderkit-email-deliverability/ directory; the skill name remains senderkit-email-deliverability.

Email authentication is required whether the app sends directly via SenderKit or routes through a provider (Resend, SendGrid, Postmark, Mailgun, SES, SMTP). This skill is provider-agnostic: it reads and fixes the DNS that controls inbox placement.

This skill does not change application code and does not edit DNS — it inspects DNS, produces records for the user to apply at their DNS host, and re-checks them. To wire sends into the codebase (From domain, headers) use senderkit-integration. To send a live test message and confirm placement use senderkit-mcp-messaging-operations.

Workflow

1. Identify the sending domain.

   • Establish the exact From domain mail is (or will be) sent from, e.g. mail.example.com or example.com.
   • If known, note the SenderKit DKIM selector and SPF include for the account; otherwise the user obtains these from the SenderKit dashboard (see step 4). Do not guess these values.

2. Diagnose current DNS. Read references/spf-dkim-dmarc.md for syntax and limits, then query:

   • SPF: dig +short TXT <domain> — flag a missing record, more than one v=spf1 record, syntax errors, and the 10-DNS-lookup limit.
   • DKIM: dig +short TXT <selector>._domainkey.<domain> — confirm the selector is published with a p= public key.
   • DMARC: dig +short TXT _dmarc.<domain> — confirm presence and policy strength (p=none vs quarantine/reject) and reporting (rua).
   • MX: dig +short MX <domain> — sanity check.
   • Alignment: confirm SPF (MAIL FROM/Return-Path) and DKIM (d=) align with the visible From domain.

3. Generate the records to add.

   • Produce the exact TXT records for the diagnosed faults (one consolidated SPF record; DKIM as published by SenderKit; a DMARC record starting at p=none for monitoring, then escalating).
   • Never produce a second v=spf1 record; merge includes into the existing one.

4. SenderKit handoff for issued values.

   • DKIM key/selector and the domain-verification token are issued when a sending domain is registered with SenderKit. There is no MCP tool for this yet — direct the user to the SenderKit dashboard/docs to copy the exact DKIM record and verification token, then add them alongside the records from step 3.
   • If a future SenderKit domain-management tool/endpoint is available at runtime, use it here to fetch the records instead of asking the user to copy them.

5. Verify.

   • Re-run the dig queries from step 2 to confirm publication. Set expectations: DNS propagation is eventually-consistent (minutes to hours); offer a re-check rather than asserting instant success.
   • Optionally suggest a manual validator (mail-tester.com, Google Postmaster Tools, MXToolbox) — these are optional and require no key.
   • Optionally use senderkit-mcp-messaging-operations to send a live test and confirm inbox placement and that headers pass SPF/DKIM/DMARC.

6. Code-side follow-ups (optional, defer depth to senderkit-integration).

   • Ensure the app From domain matches the authenticated domain.
   • Ensure List-Unsubscribe and List-Unsubscribe-Post headers are present on bulk-ish transactional mail.
   • For deeper code changes, hand off to senderkit-integration.

When a symptom is reported ("going to spam", "not arriving", "bouncing"), read references/troubleshooting.md and map symptom → cause → fix before changing records.

Reference files

• references/spf-dkim-dmarc.md - SPF/DKIM/DMARC concepts, record syntax, the 10-lookup limit, alignment, and a BIMI note.
• references/dns-provider-notes.md - Where and how to add TXT records on common DNS hosts.
• references/troubleshooting.md - Symptom → likely cause → fix for spam folder, bounces, and non-delivery.
• references/sources.md - Source notes used to build this skill.

Standards

• Diagnose before prescribing: never tell a user to add a record without first reading what is published.
• Keep exactly one SPF record per domain; stay within 10 DNS lookups.
• Recommend DMARC starting at p=none with rua reporting, then escalating to quarantine/reject after monitoring.
• Do not fabricate SenderKit DKIM selectors, SPF includes, or verification tokens; use the values SenderKit issues.
• Treat current SenderKit docs/dashboard as source of truth over this skill's static notes.