email-deliverability
This skill helps diagnose and resolve email delivery problems by configuring authentication protocols (SPF, DKIM, DMARC), monitoring sender reputation, and preventing emails from landing in spam folders. Use it when setting up email for a new domain, troubleshooting spam folder issues, customers report missing emails, configuring authentication records, migrating email providers, or conducting pre-launch deliverability audits.
git clone --depth 1 https://github.com/rampstackco/claude-skills /tmp/email-deliverability && cp -r /tmp/email-deliverability/dist/pi/.agents/skills/email-deliverability ~/.claude/skills/email-deliverabilitySKILL.md
# Email Deliverability Get email into inboxes, not spam folders. Set up authentication. Monitor reputation. Diagnose problems before they hurt the business. --- ## When to use - Setting up email for a new domain - A meaningful percentage of email is going to spam - Customers report they're not receiving emails - Setting up DMARC, SPF, or DKIM - Hardening against domain spoofing - Migrating email service providers - Sender reputation has dropped - Pre-launch audit before sending volume increases ## When NOT to use - Writing the email content itself (use `email-sequences`) - Designing the email program strategy (use `email-sequences`) - DNS records in general (use `domain-strategy`) - Outbound spam coming FROM your account (different problem; investigate compromised credentials) --- ## Required inputs - The sending domain(s) - The email service provider (ESP, transactional service, mail server) - Current DNS records (or access to them) - Email volume (transactional vs marketing, daily volume) - Current deliverability state (if known: bounce rate, spam complaints) --- ## The framework: 3 pillars Email deliverability rests on three pillars. Weakness in any one limits the others. ### Pillar 1: Authentication Mailbox providers verify email is actually from who it claims to be from. Three records. **SPF (Sender Policy Framework)** Lists which servers are authorized to send mail for the domain. Published as a TXT record at the apex. ``` v=spf1 include:_spf.mailprovider.com -all ``` - `include:` adds another sender's authorized list - `-all` (hard fail): mail from unlisted senders fails authentication - `~all` (soft fail): unlisted senders are suspicious but pass; useful during rollout - `+all`: never use; allows anyone to send Only one SPF record per domain. Multiple SPF records break SPF entirely. Combine senders into a single record. SPF has a 10-DNS-lookup limit. Each `include:` may use multiple lookups. Hit the limit and SPF stops working. Watch this carefully. **DKIM (DomainKeys Identified Mail)** A cryptographic signature on each outgoing email. The mail server signs with a private key; the public key is published in DNS. ``` selector1._domainkey.example.com TXT "v=DKIM1; k=rsa; p=MIGfMA0G..." ``` Selectors differ by ESP. Some use `default._domainkey`, some use unique selectors per service. Most ESPs walk you through publishing the records. DKIM proves the message wasn't modified in transit and that the sender controls the domain. **DMARC (Domain-based Message Authentication, Reporting, and Conformance)** The policy layer. Tells receivers what to do when SPF or DKIM fails, and where to send reports. ``` _dmarc.example.com TXT "v=DMARC1; p=reject; rua=mailto:dmarc-aggregate@example.com; ruf=mailto:dmarc-forensic@example.com; pct=100; adkim=s; aspf=s" ``` Components: - `p=`: policy. `none`, `quarantine`, or `reject`. - `rua=`: aggregate reports (daily, summary). Always set this. - `ruf=`: forensic reports (per-message). Optional, can be high volume. - `pct=`: percentage of failing mail subject to the policy. Useful for gradual rollout. - `adkim=`, `aspf=`: alignment mode. `s` (strict), `r` (relaxed). Strict means From: domain must match exactly. DMARC is the most important record. It's what makes spoofing your domain hard. ### Pillar 2: Reputation Mailbox providers (Gmail, Outlook, Yahoo) score every sender. Reputation drives delivery. Reputation factors: - **Authentication pass rates** (SPF, DKIM, DMARC) - **Engagement signals** (opens, replies, marking as not-spam) - **Negative signals** (spam complaints, deletions without opens, blocking) - **List hygiene** (low bounce rates, no spam traps) - **Volume consistency** (sudden spikes look like spam) - **Content patterns** (link reputation, attachment patterns) - **IP and domain history** Reputation is per (sending domain × mailbox provider). Gmail's view of you is independent of Outlook's. ### Pillar 3: List quality and engagement Authentication and reputation rest on list quality. Bad list = bad reputation eventually. - Only send to people who explicitly opted in - Confirmed (double) opt-in for marketing wherever feasible - Honor unsubscribes immediately and reliably - Remove hard bounces immediately - Sunset disengaged contacts (no opens in 6 months: reduce frequency or remove) - Avoid third-party lists, scraped emails, or "purchased opt-ins" The single biggest deliverability lever for most senders is list hygiene. --- ## Workflow ### Step 1: Audit current state Check the current DNS records: ```bash dig +short txt example.com dig +short txt selector1._domainkey.example.com dig +short txt _dmarc.example.com ``` Also check: - Current bounce rate (target: under 2%) - Current spam complaint rate (target: under 0.1%) - Current open rate (varies by industry; falling trend is a warning) - Current sending volume Tools: mxtoolbox.com, dmarcian.com, mail-tester.com (for individual messages). ### Step 2: Fix authentication If any of SPF, DKIM, DMARC is missing or misconfigured, fix first. **SPF fix order:** 1. Identify all legitimate senders (transactional ESP, marketing ESP, support tools, etc.) 2. Get the `include:` value or IP for each 3. Combine into a single SPF record 4. Verify lookup count is under 10 5. Use `-all` for hard fail (or `~all` if rolling out gradually) **DKIM fix order:** 1. Generate a new selector per sending service 2. Publish the public key in DNS 3. Configure the ESP to sign with the private key 4. Verify with a test send (check headers for `dkim=pass`) **DMARC fix order:** 1. Publish DMARC with `p=none` initially (monitoring mode) 2. Set up an aggregate report endpoint (use a DMARC analytics service or your own) 3. Watch reports for at least 2-4 weeks 4. Identify any legitimate senders failing alignment; fix them 5. Move to `p=quarantine` with `pct=10`, gradually increase 6. Move to `p=reject` once confidence is high The full progression typically takes 2-3 month
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