Expertise·Email

email-deliverability

Make sure email actually reaches inboxes: authentication (SPF, DKIM, DMARC), spam diagnosis, domain and sender reputation strategy, and…

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5.2k tokensestimated from the bundle, loaded when it triggers
Bundle
2 files · 20.7 kBtext throughout, nothing executable
Licence
MITpaid listing
Last change
no release on file
Servers it uses
Noneruns standalone

What it does

Make sure email actually reaches inboxes. Use this skill when setting up email authentication (SPF, DKIM, DMARC), diagnosing emails landing in spam, planning a domain reputation strategy, monitoring sender reputation, or hardening against email spoofing. Triggers on email deliverability, SPF, DKIM, DMARC, spam folder, sender reputation, mailbox provider, soft bounces, bounce rate, BIMI, MTA-STS, deliverability audit. Also triggers when a marketing or transactional email isn't reaching users.

Installed, it changes the agent in these ways.

What this skill changes about the agent is not written down here yet. The listing was collected from its source, and the description is in its own SKILL.md.

Expertise

Domain judgement the base model does not have.

emaildeliverabilitydmarcspam
Filed under

Email

The skill itself

This is the whole product. A skill is instructions the model reads, so there is nothing behind the listing you cannot see first — the front matter loads with every session, and the body below it loads when the skill triggers.

SKILL.md11.5 kB · 284 lines
--- name: email-deliverability description: "Make sure email actually reaches inboxes. Use this skill when setting up email authentication (SPF, DKIM, DMARC), diagnosing emails landing in spam, planning a domain reputation strategy, monitoring sender reputation, or hardening against email spoofing. Triggers on email deliverability, SPF, DKIM, DMARC, spam folder, sender reputation, mailbox provider, soft bounces, bounce rate, BIMI, MTA-STS, deliverability audit. Also triggers when a marketing or transactional email isn't reaching users." category: operations catalog_summary: "DMARC, SPF, DKIM, sender reputation, deliverability monitoring" display_order: 8 ---
9# Email Deliverability
10
11Get email into inboxes, not spam folders. Set up authentication. Monitor reputation. Diagnose problems before they hurt the business.
12
13---
14
15## When to use
16
17- Setting up email for a new domain
18- A meaningful percentage of email is going to spam
19- Customers report they're not receiving emails
20- Setting up DMARC, SPF, or DKIM
21- Hardening against domain spoofing
22- Migrating email service providers
23- Sender reputation has dropped
24- Pre-launch audit before sending volume increases
25
26## When NOT to use
27
28- Writing the email content itself (use email-sequences)
29- Designing the email program strategy (use email-sequences)
30- DNS records in general (use domain-strategy)
31- Outbound spam coming FROM your account (different problem; investigate compromised credentials)
32
33---
34
35## Required inputs
36
37- The sending domain(s)
38- The email service provider (ESP, transactional service, mail server)
39- Current DNS records (or access to them)
40- Email volume (transactional vs marketing, daily volume)
41- Current deliverability state (if known: bounce rate, spam complaints)
42
43---
44
45## The framework: 3 pillars
46
47Email deliverability rests on three pillars. Weakness in any one limits the others.
48
49### Pillar 1: Authentication
50
51Mailbox providers verify email is actually from who it claims to be from. Three records.
52
53**SPF (Sender Policy Framework)**
54
55Lists which servers are authorized to send mail for the domain. Published as a TXT record at the apex.
56
57```
58v=spf1 include:_spf.mailprovider.com -all
59```
60
61- include: adds another sender's authorized list
62- -all (hard fail): mail from unlisted senders fails authentication
63- ~all (soft fail): unlisted senders are suspicious but pass; useful during rollout
64- +all: never use; allows anyone to send
65
66Only one SPF record per domain. Multiple SPF records break SPF entirely. Combine senders into a single record.
67
68SPF has a 10-DNS-lookup limit. Each include: may use multiple lookups. Hit the limit and SPF stops working. Watch this carefully.
69
70**DKIM (DomainKeys Identified Mail)**
71
72A cryptographic signature on each outgoing email. The mail server signs with a private key; the public key is published in DNS.
73
74```
75selector1._domainkey.example.com TXT "v=DKIM1; k=rsa; p=MIGfMA0G..."
76```
77
78Selectors differ by ESP. Some use default._domainkey, some use unique selectors per service. Most ESPs walk you through publishing the records.
79
80DKIM proves the message wasn't modified in transit and that the sender controls the domain.
81
82**DMARC (Domain-based Message Authentication, Reporting, and Conformance)**
83
84The policy layer. Tells receivers what to do when SPF or DKIM fails, and where to send reports.
85
86```
87_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"
88```
89
90Components:
91- p=: policy. none, quarantine, or reject.
92- rua=: aggregate reports (daily, summary). Always set this.
93- ruf=: forensic reports (per-message). Optional, can be high volume.
94- pct=: percentage of failing mail subject to the policy. Useful for gradual rollout.
95- adkim=, aspf=: alignment mode. s (strict), r (relaxed). Strict means From: domain must match exactly.
96
97DMARC is the most important record. It's what makes spoofing your domain hard.
98
99### Pillar 2: Reputation
100
101Mailbox providers (Gmail, Outlook, Yahoo) score every sender. Reputation drives delivery.
102
103Reputation factors:
104- **Authentication pass rates** (SPF, DKIM, DMARC)
105- **Engagement signals** (opens, replies, marking as not-spam)
106- **Negative signals** (spam complaints, deletions without opens, blocking)
107- **List hygiene** (low bounce rates, no spam traps)
108- **Volume consistency** (sudden spikes look like spam)
109- **Content patterns** (link reputation, attachment patterns)
110- **IP and domain history**
111
112Reputation is per (sending domain × mailbox provider). Gmail's view of you is independent of Outlook's.
113
114### Pillar 3: List quality and engagement
115
116Authentication and reputation rest on list quality. Bad list = bad reputation eventually.
117
118- Only send to people who explicitly opted in
119- Confirmed (double) opt-in for marketing wherever feasible
120- Honor unsubscribes immediately and reliably
121- Remove hard bounces immediately
122- Sunset disengaged contacts (no opens in 6 months: reduce frequency or remove)
123- Avoid third-party lists, scraped emails, or "purchased opt-ins"
124
125The single biggest deliverability lever for most senders is list hygiene.
126
127---
128
129## Workflow
130
131### Step 1: Audit current state
132
133Check the current DNS records:
134
135```bash
136dig +short txt example.com
137dig +short txt selector1._domainkey.example.com
138dig +short txt _dmarc.example.com
139```
140
141Also check:
142- Current bounce rate (target: under 2%)
143- Current spam complaint rate (target: under 0.1%)
144- Current open rate (varies by industry; falling trend is a warning)
145- Current sending volume
146
147Tools: mxtoolbox.com, dmarcian.com, mail-tester.com (for individual messages).
148
149### Step 2: Fix authentication
150
151If any of SPF, DKIM, DMARC is missing or misconfigured, fix first.
152
153**SPF fix order:**
1541. Identify all legitimate senders (transactional ESP, marketing ESP, support tools, etc.)
1552. Get the include: value or IP for each
1563. Combine into a single SPF record
1574. Verify lookup count is under 10
1585. Use -all for hard fail (or ~all if rolling out gradually)
159
160**DKIM fix order:**
1611. Generate a new selector per sending service
1622. Publish the public key in DNS
1633. Configure the ESP to sign with the private key
1644. Verify with a test send (check headers for dkim=pass)
165
166**DMARC fix order:**
1671. Publish DMARC with p=none initially (monitoring mode)
1682. Set up an aggregate report endpoint (use a DMARC analytics service or your own)
1693. Watch reports for at least 2-4 weeks
1704. Identify any legitimate senders failing alignment; fix them
1715. Move to p=quarantine with pct=10, gradually increase
1726. Move to p=reject once confidence is high
173
174The full progression typically takes 2-3 months. Rushing causes legitimate mail to bounce.
175
176### Step 3: Set up monitoring
177
178Ongoing visibility:
179
180- **DMARC aggregate reports**: parsed daily. Watch for new sources, alignment failures, volume changes.
181- **Bounce rate**: per ESP dashboard. Target under 2% for transactional, under 5% for marketing.
182- **Spam complaint rate**: target under 0.1%.
183- **Reputation tools**: Google Postmaster Tools (free), Microsoft SNDS, Talos, Sender Score.
184- **Blacklist monitoring**: most ESPs include this; otherwise mxtoolbox.com or hetrixtools.com.
185
186### Step 4: Address list hygiene
187
188- Remove hard bounces from your sending lists immediately (most ESPs do this; verify)
189- Set up suppression lists (unsubscribes, manual blocks, deliverability sinkholes)
190- Sunset disengaged contacts (re-engagement campaigns or just remove)
191- Review opt-in flows: do people know what they're signing up for?
192
193### Step 5: Content and pattern audit
194
195If reputation is good and authentication passes, check content:
196
197- HTML-only emails (no plain-text alternative) raise flags
198- Heavy image-to-text ratios raise flags
199- Suspicious link patterns (bare IPs, URL shorteners, hijacked domains)
200- Specific spam-trigger words in subject lines (less important than it used to be, still real)
201- Lots of mismatched domains in URLs
202- Generic from-name like "info@" rather than a real-sounding sender
203
204### Step 6: Plan for growth
205
206Email volume affects reputation. Sudden spikes look like spam.
207
208- Warm up new sending IPs gradually (start at 50/day, 2x daily)
209- Warm up new domains gradually (similar pattern)
210- Spread sends throughout the day
211- Don't switch ESPs the week before a big launch
212
213### Step 7: Set up BIMI (optional but valuable)
214
215BIMI (Brand Indicators for Message Identification) shows your logo next to authenticated emails in supporting clients (Gmail, Apple Mail, Yahoo, others).
216
217Requires:
218- DMARC at p=quarantine or p=reject (so this comes after the DMARC progression)
219- A trademarked logo as an SVG (specific format requirements)
220- A Verified Mark Certificate (VMC) from a CA, for Gmail and others
221- A _bimi DNS record pointing to the SVG and VMC
222
223BIMI improves trust signals and engagement. Worth doing once DMARC enforcement is in place.
224
225### Step 8: Document and revisit
226
227Document the email architecture:
228- Sending domains and subdomains
229- Each ESP and what it sends
230- DNS records for each
231- Monitoring setup
232- Escalation if deliverability degrades
233
234Revisit quarterly or when a new ESP is added.
235
236---
237
238## Failure patterns
239
240**Multiple SPF records.** Two or more SPF records on the same domain breaks SPF. Combine into one.
241
242**SPF DNS lookup limit exceeded.** Too many include: directives or chained includes. Flatten or simplify.
243
244**DMARC at p=none forever.** Monitoring without enforcement. Spoofing remains easy. Move to enforcement.
245
246**DMARC at p=reject too quickly.** Legitimate mail bounces because alignment wasn't verified. Use the gradual rollout.
247
248**Sending from a different domain than the From: address.** Causes alignment failures. Fix the From: domain or ensure proper alignment.
249
250**Using a shared ESP IP without ESP-specific configuration.** Some ESPs don't sign with your DKIM by default; the signature is the ESP's, not yours. Configure custom DKIM.
251
252**Sending from a domain that also sends marketing.** A spam complaint on a marketing email hurts transactional deliverability. Use a subdomain for transactional (transactional.example.com) or marketing (mail.example.com).
253
254**No bounce monitoring.** Hard bounces accumulate, reputation tanks, deliverability cliff-falls. Monitor.
255
256**Bought lists or scraped contacts.** Spam traps in those lists destroy reputation. Don't.
257
258**No double opt-in for marketing.** Single opt-in lets bots and typos onto the list. Bots generate spam complaints, destroy reputation.
259
260**Ignoring DMARC reports.** Reports show problems early. Set up a parser. Look weekly.
261
262**Treating "marked as not-spam" as the goal.** The goal is to never land in spam in the first place. Once reputation is bad, recovery takes months.
263
264---
265
266## Output format
267
268A deliverability audit document includes:
269
270- **Domain inventory:** every sending domain
271- **Authentication status:** SPF, DKIM, DMARC per domain
272- **Sender inventory:** every ESP or service that sends mail, what's configured
273- **Reputation status:** per major mailbox provider where measurable
274- **List hygiene:** bounce rate, complaint rate, opt-in process
275- **Findings:** prioritized issues
276- **Roadmap:** SPF/DKIM/DMARC fixes, BIMI plan, monitoring plan
277- **Monitoring setup:** what's watched, where alerts go
278
279---
280
281## Reference files
282
283- [references/dmarc-rollout-playbook.md](references/dmarc-rollout-playbook.md): Step-by-step for moving from no DMARC to p=reject, with timing, monitoring, and how to handle problems found along the way.
284
In the file
SKILL.md1,678 words
Files2
LicenceMIT
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If this is not it

13 other skills in Email

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  • SKILL.md11.5 kB
  • references/dmarc-rollout-playbook.md9.2 kB
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$29 once
email-deliverability · MIT · rampstackco
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Price$29 once
LicenceMIT — the author’s, unchanged by this purchase
Paid throughStripe, once, on the card you add at the checkout
Keeps workingfor good — the files are yours once they are on disk
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