Twilio Sendgrid Deliverability Advisor

When to use

Use this when mail is being sent but under-performing — landing in spam, bouncing, or throttled — and you need a structured read on why and what to change to get into the inbox.

Not for: first-time account/domain setup (see twilio-sendgrid-account-setup) or interpreting engagement metrics for content quality (see twilio-sendgrid-engagement-quality).

Method

1. Confirm authentication alignment first — it is the most common root cause. Verify SPF passes, DKIM signs with your domain, and DMARC aligns (the From domain matches the authenticated domain). Misalignment sends good mail to spam regardless of content.
2. Check DMARC posture. At p=none you only monitor; move toward p=quarantine/p=reject once aggregate reports confirm all legitimate sources align.
3. Read the numbers: pull Stats and reputation. Watch bounce rate (keep well under ~2%), spam-complaint rate (keep under ~0.1%), and the account/IP reputation score. These are the thresholds receivers punish.
4. Assess IP strategy. On shared IPs you inherit pool reputation; on a dedicated IP you own it and must warm up — ramp volume gradually over days/weeks so receivers build trust. A cold dedicated IP blasted at full volume gets throttled.
5. Segment by engagement. Sending to unengaged/old addresses drags reputation; send to recent openers/clickers first and sunset dead contacts.
6. Audit content: excessive links, image-only mail, spammy phrasing, URL shorteners, and unbranded (sendgrid.net) links depress placement. Use link branding and balanced text/HTML.
7. Check blocklists and seed-test. If reputation dropped suddenly, check major blocklists for your domain/IP and run inbox-placement seed tests across providers.

Example

Pull the signals that most often explain spam-foldering:

# Global stats for the window (bounces, spam reports, delivered)
curl -sS "https://api.sendgrid.com/v3/stats?start_date=2026-07-01&aggregated_by=day" \
  -H "Authorization: Bearer $SENDGRID_API_KEY"

Then triage: DKIM/SPF/DMARC aligned? bounce < 2%? complaint < 0.1%? links branded? If all pass yet Gmail spam-folders, the cause is usually low engagement or a cold IP — segment to engaged recipients and slow the ramp.

Pitfalls

• Blaming content when auth is broken. Rewriting copy will not fix DMARC misalignment. Verify SPF/DKIM/DMARC before touching the message.
• Blasting a cold dedicated IP. No warm-up means receivers see a sudden stranger at volume and throttle/block. Ramp gradually.
• Ignoring the complaint rate. Even ~0.1% spam complaints signals receivers to demote you. Prune and honor opt-outs aggressively.
• Sending to stale lists. Old, unengaged addresses generate bounces and spam-trap hits that tank reputation. Sunset non-openers.
• Unbranded links. sendgrid.net click links share pooled reputation; brand your link domain.

Output format

# Deliverability Review: <domain/stream>
AUTH: SPF=pass DKIM=pass(domain) DMARC=aligned policy=<none/quarantine/reject>
REPUTATION: score=<n> bounce=<%> complaint=<%>  [thresholds: bounce<2%, complaint<0.1%]
IP: <shared|dedicated> warmup=<stage/NA>
LIST: engagement segmentation=<yes/no> stale sunset=<yes/no>
CONTENT: link-branding=<on/off> flags=[<image-only|shorteners|...>]
BLOCKLIST: <clear | listed on ...>
TOP FIXES: 1) ... 2) ... 3) ...

Reference

• Stats/reputation: /v3/stats, /v3/categories/stats, and reputation surfaced in the console; suppression signals via /v3/suppression/*.
• Authentication: SPF + DKIM (from Domain Authentication) plus DMARC alignment (From domain = authenticated domain) is the deliverability foundation; DMARC aggregate reports (rua) reveal misaligned sources.
• Receiver thresholds to respect: bounce rate < ~2%, spam-complaint rate < ~0.1%; dedicated IPs require gradual warm-up.
• Event Webhook bounce/spamreport data (see twilio-sendgrid-webhooks) is the raw feed for these diagnostics.