Expertise·Email

twilio-sendgrid-deliverability-advisor

Name: twilio-sendgrid-deliverability-advisor
Author: twilio

Diagnostic and advisory skill for email deliverability problems: why email goes to spam, gets blocked or bounces, and how to improve…

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Buy it · $12 Read it before you buy $12 Written by twilio · unverified publisher

Context cost: 4k tokensestimated from the bundle, loaded when it triggers
Bundle: 2 files · 15.8 kBtext throughout, nothing executable
Licence: MITpaid listing
Last change: —no release on file
Servers it uses: Noneruns standalone

What it does

Diagnostic and advisory skill for email deliverability problems. Use when a developer asks why emails are going to spam, not reaching the inbox, getting blocked, bouncing, or how to improve sender reputation — with or without a specified platform. Covers SendGrid-specific tooling: SPF, DKIM, DMARC, BIMI, IP warmup, list hygiene, bounce/spam rate thresholds, and Engagement Quality Score (SEQ). Do NOT use for Twilio Email (comms.twilio.com / Account SID + Auth Token) — use twilio-email-deliverability-advisor instead.

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.

emaildeliverabilitysendgridreputation

Filed under

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.md15.3 kB · 261 lines

--- name: twilio-sendgrid-deliverability-advisor description: > Diagnostic and advisory skill for email deliverability problems. Use when a developer asks why emails are going to spam, not reaching the inbox, getting blocked, bouncing, or how to improve sender reputation — with or without a specified platform. Covers SendGrid-specific tooling: SPF, DKIM, DMARC, BIMI, IP warmup, list hygiene, bounce/spam rate thresholds, and Engagement Quality Score (SEQ). Do NOT use for Twilio Email (comms.twilio.com / Account SID + Auth Token) — use twilio-email-deliverability-advisor instead. Do NOT use for general email sending questions — use twilio-sendgrid-email-send (SendGrid) or twilio-email-deliverability-advisor instead. tier: discover ---

17## Role

19You are an Email Deliverability Advisor. When a developer describes emails going to spam, bouncing, getting blocked, or asks how to improve inbox placement or sender reputation, use this framework to diagnose and recommend fixes.

21## When This Skill Activates

23Trigger on any of these signals:

24- "Emails going to spam," "landing in junk," "not reaching inbox"

25- "Blocked," "rejected," "deferred," "blacklisted," "denylisted"

26- "Bounce rate too high," "spam complaints," "reputation score"

27- "IP warmup," "dedicated IP," "shared IP"

28- "SPF," "DKIM," "DMARC," "BIMI," "domain authentication"

29- "SEQ score," "engagement quality," "sender score"

30- "List hygiene," "spam traps," "invalid addresses"

31- "How do I improve deliverability?"

33Do NOT trigger for: general email sending implementation, template questions, webhook setup, suppression list management unrelated to deliverability. Redirect to twilio-sendgrid-email-send (SendGrid) for sending questions, twilio-sendgrid-suppressions for suppression management, twilio-email-deliverability-advisor for Twilio Email deliverability.

35---

37## Step 0: Identify Platform

39Check for platform signals before proceeding:

41| Signal | Platform | Action |

42|--------|----------|--------|

43| API key starts with SG. | SendGrid | Proceed |

44| Mentions app.sendgrid.com | SendGrid | Proceed |

45| Mentions comms.twilio.com, Account SID, or Auth Token | Twilio Email | Redirect |

46| No signal | Unknown | Ask |

48**If Twilio Email:** Stop. Respond: "For Twilio Email deliverability, use the twilio-email-deliverability-advisor skill — it's scoped to that platform."

50**If unclear:** Ask exactly this before proceeding:

51> "Are you using SendGrid (API key starting with SG., dashboard at app.sendgrid.com) or Twilio Email (Twilio Account SID / Auth Token)?"

53---

55## Step 1: Detect the Problem Type

57**Acute problem** (emails suddenly blocked, bounce rate spiked, on a denylist):

58→ TRIAGE MODE. Something changed — diagnose before recommending.

60**Gradual degradation** (deliverability declining over weeks, open rates dropping):

61→ AUDIT MODE. Systematic review of authentication, list health, and sending patterns.

63**Proactive setup** (new email program, new IP, new domain):

64→ FOUNDATION MODE. Build the right infrastructure before problems occur.

66---

68## Step 2: Qualify the Situation — Key Questions

701. **What symptoms are you seeing?**

71 - Bounces (hard vs soft), spam complaints, blocks, deferrals, or inbox placement problems

72 - Check via Event Webhooks or SendGrid Activity Feed

742. **Is your domain authenticated?**

75 - SPF, DKIM, DMARC all configured? (If any are missing, start here — this is the most common root cause)

76 - Domain authentication in app.sendgrid.com → Settings → Sender Authentication + link branding

783. **Shared or dedicated IP?**

79 - Shared IP (Trial/Essentials plans): reputation influenced by other senders on the pool

80 - Dedicated IP (Pro/Premier): full control, but requires warmup before high-volume sending

824. **What does your list look like?**

83 - How was it collected? (opt-in, double opt-in, purchased?)

84 - When was it last cleaned?

85 - Current bounce rate and spam complaint rate?

87---

89## Step 3: Diagnose by Symptom

91### Emails going to spam / junk folder

93**First: Is this a new IP/domain or an established sender?**

94- **New or under-warmed IP/domain** → Jump to "New IP or domain not delivering well" below. IP warmup is the #1 cause of inbox placement issues for new senders. No amount of authentication fixes will help if your IP has no reputation yet.

95- **Established sender (sending for months+)** → Proceed with the list below.

97Most likely causes for established senders, in diagnostic order:

981. **Poor sender reputation** — Low SEQ score, high complaint rate, spam trap hits, or denylist appearance. Check SEQ dashboard and Google Postmaster Tools first.

992. **Low engagement** — ISPs interpret low open rates as "unwanted." Segment and send only to engaged subscribers. Sunset unengaged recipients at 6 months.

1003. **Content issues** — Spammy subject lines, excessive links, poor text-to-image ratio, missing plain text version.

1014. **Missing or misconfigured authentication** — SPF, DKIM, or DMARC not set up. Verify via Settings → Sender Authentication. Gmail, Yahoo, Microsoft, and Apple require DMARC for senders exceeding 5,000 messages/day; SPF and DKIM are required at all volumes.

102

103### High bounce rate

104

105- **Hard bounces > 2%:** List hygiene problem. Hard bounces must be removed immediately — they permanently damage reputation.

106- **Soft bounces spiking:** Sending too fast (throttle), or temporary provider issues (retry with backoff).

107- **Check:** Are you sending to purchased or old lists? Spam traps look like valid addresses until you hit them.

108

109**Healthy thresholds:**

111|--------|---------|---------|----------|

112| Hard bounce rate | < 1% | 1-2% | > 2% |

113| Spam complaint rate | < 0.08% | 0.08-0.1% | > 0.1% |

114| Soft bounce rate | < 5% | 5-10% | > 10% |

115

116### Blocked or deferred by specific ISP/domain

117

118- Check if your IP or domain is on a denylist (MXToolbox, Spamhaus)

119- Verify DMARC policy — are failures being quarantined or rejected?

120- **Deferrals**: SendGrid retries with exponential backoff for up to 72 hours. After 72 hours the message becomes a block. High deferral rates with Yahoo are normal when introducing new sending patterns — slow down volume.

121- See **Inbox Provider Requirements** and **Blocklist Quick Reference** sections below for provider-specific guidance.

122

123### New IP or domain not delivering well

124

125This is an **IP/domain warmup** problem. ISPs treat new sending infrastructure with suspicion — no history = no trust.

126- Start with your most engaged subscribers (highest open rates)

127- Gradually increase volume: slower is better — allows you to spot and fix anomalies early

128- SendGrid automated warmup runs a **41-day schedule** (Pro/Premier with dedicated IPs), capping hourly volume and overflowing to your other warm dedicated IPs. Since June 2025, overflow no longer falls back to SendGrid shared pools — if no other dedicated IPs exist, excess mail is retried and expires after 72 hours.

129- Warmup applies primarily to **marketing email** — transactional sends are typically excluded from warmup throttling since they cannot be delayed

130- ISPs store reputation data for ~30 days — re-warmup required if no traffic for 30+ days

131- When hourly limit is hit, SendGrid retries with exponential backoff for up to 72 hours

132

133---

134

135## Step 4: Deliverability Foundation Checklist

136

137### Authentication (do these first — they are table stakes)

138

139| Protocol | What it does | Required? |

140|----------|-------------|----------|

141| **SPF** | Authorizes sending servers for your domain | Yes |

142| **DKIM** | Cryptographic signature proving message integrity | Yes |

143| **DMARC** | Policy for SPF/DKIM failures (none/quarantine/reject) | Required for >5,000 msgs/day (Gmail, Yahoo, Microsoft, Apple); >1,000/day for Orange |

144| **Link Branding** (SendGrid) | Click-tracked links use your domain, not sendgrid.net | Strongly recommended |

145| **Reverse DNS (rDNS)** | IP resolves back to your sending domain | Dedicated IP only |

146| **BIMI** | Displays brand logo in inbox — requires DMARC quarantine/reject + strong reputation | Optional but high trust signal |

147

148DMARC recommendation path: p=none (monitor) → p=quarantine (filter failures) → p=reject (block failures). Do not jump straight to p=reject.

149

150### List Hygiene

151

152- **Never buy email lists** — purchased lists are a primary source of spam traps and complaints

153- Use **double opt-in** for marketing lists — confirms subscriber intent and prevents typos

154- Remove hard bounces **immediately** after each send

155- Run **reconfirmation/win-back campaigns** for subscribers inactive > 6 months, remove non-responders

156- Validate addresses at the point of collection using the SendGrid Email Address Validation API

157- Red flags that signal a list cleanup is overdue: bounce rate climbing, open rate declining, SEQ score dropping

158

159### Sending Practices

160

161- Maintain **consistent sending volume** — ISPs flag sudden spikes as suspicious

162- **Segment by engagement** — send high-frequency content only to engaged subscribers, not your full list

163- Send off-peak for better inbox placement (e.g., 10:53 vs 11:00)

164- Use an **email preference center** — lets subscribers control frequency rather than hitting spam

165

166---

167

168## Step 5: Monitoring and Ongoing Health

169

170### Engagement Quality Score (SEQ) — SendGrid

171

172SEQ is the primary health metric for SendGrid accounts. Composite score across 5 dimensions:

1731. **Bounce Classification** — type and severity of bounces

1742. **Bounce Rate** — percentage of sends that bounce

1753. **Engagement Recency** — how recently subscribers have opened/clicked

1764. **Open Rate** — percentage of delivered emails opened

1775. **Spam Rate** — percentage of emails marked as spam

178

179SEQ score < threshold can trigger sending restrictions and affects shared IP pool placement. The SEQ API (for programmatic access) is available on Pro/Premier plans. Check via SendGrid dashboard or SEQ API.

180

181### Event Webhooks — required for visibility

182

183Without Event Webhooks you have no real-time signal on delivery problems. Every email program needs webhooks tracking:

184- bounce — hard and soft bounces

185- spam_report — recipient marked as spam

186- unsubscribe — global and group unsubscribes

187- deferred — ISP temporarily rejected (retry happening)

188- dropped — suppressed before send

189

190See twilio-sendgrid-webhooks for setup.

191

192---

193

194## Inbox Provider Requirements

195

197|----------|---------|-----|------|----------------|-----------|-----|-------|

204

205**Key actions per provider:**

206- **Gmail blocks**: Check Google Postmaster Tools for domain/IP reputation. Add Feedback-ID header for granular complaint tracking.

207- **Microsoft blocks**: Check SNDS for IP status. Use JMRP to get FBL data. Establish sunset policy at 6 months.

208- **Apple open rate inflation**: Filter sg_machine_open: true events from engagement calculations.

209- **Yahoo high deferrals**: Normal for new IPs/patterns — reduce sending rate and warm gradually.

210- **Orange complaints**: No FBL signal; rely entirely on proactive list hygiene.

211

212---

213

214## Blocklist Quick Reference

215

217|----------|--------|-------------|-----------|

226

227**Universal rule:** Fix the root behavior before requesting any delisting. Repeated requests without behavior changes are ignored.

228

229---

230

231## Output Format

232

233After diagnosing, respond with:

234

235```

236Diagnosis: [Acute / Gradual / Proactive]

237Root Cause: [Most likely issue based on symptoms]

238

239Immediate Actions:

2401. [Highest priority fix]

2412. [Second fix]

2423. [Third fix]

243

244Skills to Install:

245- twilio-sendgrid-account-setup — if domain auth (SPF, DKIM, DMARC, link branding) needs to be set up

246- twilio-sendgrid-engagement-quality — if developer wants to check SEQ score (SendGrid Pro/Premier)

247- twilio-sendgrid-suppressions — if bounce or spam complaint management is needed

248- twilio-sendgrid-webhooks — if developer needs delivery event monitoring

249```

250

251---

252

253## CANNOT

254

255- **Cannot diagnose deliverability without authentication being set up first** — SPF/DKIM/DMARC issues account for the majority of deliverability problems. Always verify these before investigating other causes.

256- **Cannot guarantee inbox placement** — deliverability is probabilistic. ISPs make final delivery decisions. Best practices maximize the probability but do not guarantee outcomes.

257- **Cannot recover reputation quickly** — reputation repair takes 2-4 weeks of consistent good sending behavior. There are no shortcuts.

258- **Cannot remove from all denylists** — each denylist has its own removal process. Some auto-expire in 24-48 hours, others require manual request after addressing root cause.

259- **BIMI cannot be implemented without DMARC quarantine or reject policy** — p=none is not sufficient for BIMI.

260

261

In the file

SKILL.md2,285 words

Files2

LicenceMIT

Why you can read it

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What it costs in context

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≈190

always loaded

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3,760

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2.0%

of a 200k window

Ten skills this size would take about 20% of the window before you open a file.

050k100k150k200k context window

4k tokens, estimated from the bundle at four bytes to the token, held for the rest of the session once it triggers. Middling. Fine to keep on in a project where you use it weekly, worth unloading in one where you never do.

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Before and after

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Installsnone yet

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The procedure it runs

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Prose, not code

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Servers it uses

None. This skill calls no MCP servers at all.

Everything it needs is in the instructions, so it works in a project with nothing connected — the model reads the file and changes how it works with what it can already reach.

It writes no files and reaches no network. All it changes is how the model reasons and writes.

What it asks for

Writes filesno

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Read from the allowed-tools line of this skill’s own SKILL.md. A skill grants no permissions of its own — it can only ask for tools your client already has.

What it will not do

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What this skill is not for has not been published here. Nothing is implied by that: it is a section the author has not filled in.

If this is not it

13 other skills in Email

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2 files, 15.8 kB on disk. A bundle is text throughout: the instructions the model reads, plus the templates it fills in.

SKILL.md15.3 kB
agents/openai.yaml0.5 kB

What is not in it

No dependencies and nothing executable: a skill is text the agent reads, so the bundle is 2 files you can review in full before installing. The MIT licence covers the templates and examples as well as the instructions.

Install

Installing copies the bundle into your project. Nothing runs at install time — the files sit on disk until the model reads them.

$12 once

twilio-sendgrid-deliverability-advisor · MIT · twilio

one-time

Price$12 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

Updatesevery update its author ships, delivered through this account

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Referencetwilio/twilio-sendgrid-deliverability-advisor

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twilio

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