An email deliverability audit checks what decides inbox placement: authentication (SPF, DKIM and DMARC aligned to your From domain), reputation (spam complaints under 0.3%, ideally under 0.1%), list hygiene (bounces under 2%) and sending behavior. Since 2024, Gmail, Yahoo and Microsoft reject or junk bulk mail that misses these rules.
Look up your live records with dig TXT yourdomain.com and dig TXT _dmarc.yourdomain.com. Nested includes are counted only one level deep here; the full count can be higher.
If you send about 5,000+ messages a day to consumer mailboxes, these are pass/fail rules now, not best practices. B2B teams hit them through newsletters, webinars and product email.
| Requirement | Gmail | Yahoo / AOL | Microsoft (Outlook.com) |
|---|---|---|---|
| Who it applies to | About 5,000+ messages/day to personal Gmail accounts | Bulk senders; no volume published, so treat sustained marketing mail as in scope | Domains sending 5,000+ messages/day to Outlook.com, Hotmail and Live |
| SPF | Required | Required | Required |
| DKIM | Required | Required | Required |
| DMARC | Required, p=none minimum | Required, p=none minimum | Required, p=none minimum |
| Alignment with the From domain | Required (SPF or DKIM) | Required (SPF or DKIM) | Required (SPF or DKIM) |
| One-click unsubscribe (RFC 8058) | Required on marketing mail | Required on marketing mail | Working unsubscribe expected; header recommended |
| Honor unsubscribes | Within 2 days | Within 2 days | Not specified |
| Spam complaint rate | Under 0.3%; aim under 0.1% | Under 0.3% | No published threshold |
| PTR / reverse DNS | Required | Expected | Required |
| TLS | Required | Recommended | Recommended |
| Enforcement | Phased from Feb 2024; non-compliant bulk mail rejected at SMTP since Nov 2025 | Since Feb 2024 | Since May 5, 2025; rejects with 550 5.7.515 |
Sources: Google Email sender guidelines and bulk sender FAQ, Yahoo Sender Hub best practices, and Microsoft’s May 2025 Outlook.com requirements, as summarized by Mailsoftly (provider table checked October 18, 2026) and PowerDMARC (updated June 2026). Gmail’s bulk rules are written for personal accounts; Google Workspace inboxes still filter on the same authentication and complaint signals, so B2B senders should meet them anyway. Every sender, at any volume, needs SPF or DKIM, valid PTR records, TLS and a complaint rate under 0.3% for Gmail.
Authentication fails quietly. A record can “pass” a basic checker and still fail DMARC because it isn’t aligned with the domain your recipients see.
v=spf1 include:_spf.google.com include:[your-esp-include] -all
_dmarc.yourdomain.com TXT v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com; adkim=r; aspf=r; sp=quarantine; fo=1
HubSpot senders: connect your email sending domain in HubSpot and publish the DKIM records it gives you. That gives you aligned DKIM, which is what DMARC needs. Outbound tools (Outreach, Salesloft, Apollo, lemlist and similar) send through your mailboxes, so they follow your Google Workspace or Microsoft 365 authentication; secondary domains for cold outbound need their own SPF, DKIM, DMARC and warm-up. Our Digital Identity Migration page covers domain warm-up.
Start from what you’re seeing. Each symptom maps to a short list of causes and one first check that settles which one it is.
| Symptom | Likely causes | First check | Fix |
|---|---|---|---|
| Hard bounces with 550 5.7.26 or 550 5.7.515 | DMARC fails: SPF or DKIM missing, or not aligned with the From domain | Message headers: Authentication-Results for dmarc=fail | Turn on DKIM with your domain in the sending tool; fix SPF includes; publish DMARC |
| Open rates fell off a cliff overnight | Provider started junking or rejecting; domain or IP blocklisted; tracking domain flagged | Postmaster Tools spam rate and compliance status; blocklist lookup | Pause bulk sends, fix authentication, delist, resume with engaged segments only |
| Gmail lands in spam, Outlook is fine (or vice versa) | Provider-specific reputation; complaint rate high at one provider; missing one-click unsubscribe | Split results by recipient domain in your ESP | Suppress non-engagers at that provider; add RFC 8058 headers; slow volume while reputation recovers |
| HubSpot emails go to spam, Gmail-to-Gmail doesn’t | HubSpot sending domain not connected (no aligned DKIM); shared link-tracking domain | Domains settings in HubSpot; DKIM d= in headers | Connect the sending domain, publish DKIM records, set a branded tracking domain |
| Cold outbound replies dried up | Too many sends per mailbox; new domains not warmed; spam-trap or role addresses on lists; link-heavy copy | Sends per mailbox per day; list source; bounce rate by sequence | Cap volume per mailbox, verify lists before upload, warm new domains, plain-text first touches |
| Bounce rate above 2% | Old or purchased lists; no verification on import; enrichment returning guessed emails | Bounce rate by list source and import date | Verify before send, sunset contacts with no engagement in 6–12 months, fix enrichment waterfall |
| Spam complaints above 0.1% | Unclear consent; hard-to-find unsubscribe; frequency spikes; irrelevant segments | Complaint rate by campaign and segment | One-click unsubscribe, preference center, frequency caps, tighter segments |
| Messages delayed or deferred (4xx codes) | Rate limiting from sudden volume spikes or new IPs; reputation warning signs | ESP delivery logs for 421 deferrals by provider | Smooth send volume, warm new IPs gradually, investigate before it becomes 5xx |
| Internal email to colleagues lands in junk | Your own DMARC or SPF is broken; a third-party tool sends as your domain without authentication | DMARC aggregate reports for unknown sources | Authorize or shut down the unknown sender; correct SPF; keep DMARC at p=none until clean |
Use these bands to triage, then watch the trend. A program moving from strong to acceptable is a warning even before it breaks.
| Metric | Weak | Acceptable | Strong | Basis |
|---|---|---|---|---|
| Spam complaint rate (Postmaster Tools) | ≥ 0.3% | 0.1–0.3% | < 0.1% | Gmail / Yahoo thresholds |
| Hard bounce rate per send | > 2% | 0.5–2% | < 0.5% | JayOh guidance |
| DMARC policy | None published | p=none with reports read | p=quarantine or p=reject | Provider minimum is p=none |
| Messages passing aligned DMARC | < 90% | 90–98% | > 98% | JayOh guidance, from DMARC reports |
| Cold sends per mailbox per day | > 100 | 50–100 | ≤ 50 | JayOh guidance for outbound |
| Cold outbound reply rate | < 1% | 1–5% | > 5% | JayOh guidance; Airhouse reached 8%+ after fixes |
| Contacts with no engagement in 12 months still mailed | > 30% of list | 10–30% | < 10% | JayOh guidance |
Open rates are left out on purpose. Apple Mail Privacy Protection inflates opens, so use replies, clicks, complaints and Postmaster data instead. Bands marked “JayOh guidance” are working ranges from our audits, not third-party survey data.
Twelve questions across authentication, reputation, list hygiene and sending behavior. Answer for your main sending domain.
Higher is healthier. Unanswered counts as zero.
Fix in this orderBuilt for marketing ops and demand gen teams who need inbox placement back before the next campaign, not a six-month retainer.
Runs as a Mini Bucket of Hours: 20 hours, one-time, used inside a 70-day window. Implementation can continue on the same bucket or a partner plan.
Our audit of Airhouse’s outbound found authentication gaps and content risks. After fixes and list cleanup, campaigns sustained 30%+ open rates and 8%+ reply rates, with a measurable drop in bounces.
Case studyThe pattern we see most: deliverability lives in one ops person’s head. When they leave, monitoring stops and nobody notices until a campaign lands in spam. The audit leaves a written owner map and checklist.
Common triggerA fraud-prevention platform we audited years ago came back for a pulse check after rebranding to a new domain, the moment authentication most often breaks across every sending tool.
Returning clientDNS, platforms, lists and sending behavior sit with four different owners. Our pod works across all of them, so the fix doesn’t stall between IT and marketing.
We engineer growth systems. JayOh builds the RevOps architecture, GTM execution and data infrastructure that turn messy revenue operations into predictable pipeline for B2B SaaS and PE-backed teams.
