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Gmail and Outlook rewrote the rules in 2024. Half of existing cold-email setups quietly lost 30-50% deliverability and most operators still don't know why. Here's the 2026 deliverability checklist for Lemlist.
Who this is forOperators running active Lemlist campaigns who suspect deliverability is degraded — open rates trending down, replies trending down, more 'I didn't see your email' on calls. Also relevant for anyone setting up new infrastructure who wants to start clean.
What you'll need
Step 1
Gmail and Yahoo now enforce strict DMARC for any sender doing 5,000+ emails/day. Outlook is stricter than ever on SPF alignment. Audit at mxtoolbox.com.
Open mxtoolbox.com → Domain Health. Run a full scan on your sending domain.
SPF: must be exactly one TXT record. Multiple SPF records = automatic fail. Maximum 10 DNS lookups in the chain.
DKIM: 2048-bit key recommended. 1024-bit is increasingly flagged. Verify by sending to check-auth@verifier.port25.com — should return pass.
DMARC: must exist. `p=none` is acceptable but `p=quarantine` is preferred. Include `rua=mailto:reports@yourdomain.co` for aggregate reports.
BIMI (optional, advanced): if you have a verified VMC, BIMI adds your logo to inbox — increases trust signals at Gmail.
Fix any DNS issues immediately. Bad DNS is the #1 cause of new-account deliverability failure in 2026.
Step 2
Modern spam filters care less about specific words and more about overall pattern: link density, image-to-text ratio, all-caps, urgency words.
Test every email template via mail-tester.com. Aim for 9+/10 score before launching at scale.
Avoid all-caps subject lines or words ("URGENT", "ACT NOW") — automatic spam-bin in most filters.
Link density: max 1 link per 100 words of body content. More than 2 links in a 150-word email looks promotional.
Image-to-text ratio: text should be 60%+ of total content. Image-only emails trigger automatic spam routing.
Avoid unsubscribe-list-like patterns: no 'click here to unsubscribe' boilerplate in cold (you don't need it for true cold under CAN-SPAM, but many filter heuristics look for the pattern).
Subject line length: 30-50 characters is optimal. Too short looks empty; too long gets truncated and looks generic.
First line of body: never start with 'My name is...' or 'I'm reaching out from...' — these are pattern-matched to cold-spam.
Step 3
Sending to invalid emails is the fastest way to burn reputation. Verify every list before importing into Lemlist.
Run every CSV through an email verifier: NeverBounce, ZeroBounce, Bouncer, or Apollo's built-in verifier.
Remove: invalid emails, catch-all unconfirmed, role-based addresses (info@, sales@), and 'risky' status leads.
Target: under 2% bounce rate per campaign. Above 5% triggers ESP throttling. Above 10% gets your mailbox suspended.
Re-verify lists older than 60 days. People change jobs. Emails go stale. A list that was 95% valid 6 months ago might be 75% valid now.
For high-stakes campaigns (under 100 leads to enterprise), verify each lead manually via LinkedIn — confirm they're still at the company.
Step 4
Even with perfect setup, sending too much too fast tanks reputation. Use Lemlist sending caps and inbox rotation.
Per-mailbox daily cap: 30-50 cold emails/day MAX. Yes, Google allows 2,000/day technically. But spam filter tolerance for cold-pattern sending is much lower.
In Lemlist → Settings → Sending → Sending limits, set daily cap to 35/day per mailbox.
Enable 'Inbox rotation' to distribute one campaign across multiple connected mailboxes. Doubles your safe daily volume without overloading any single mailbox.
Stagger sends: don't blast 35 emails at 9:01am. Spread across 8-10 hours with random intervals. Lemlist's default human-like sending does this automatically.
Send Mon-Thu primarily. Friday afternoon and weekends have higher spam-filter scrutiny because legitimate business email volume drops.
Respect time zones: send between 8am-5pm in the prospect's local time. Lemlist's 'Send in lead timezone' setting handles this automatically if your CSV has timezone data.
Step 5
Google Postmaster Tools shows your domain reputation from Gmail's perspective. Free, essential, and most operators don't use it.
Set up Google Postmaster Tools (postmaster.google.com). Verify your sending domain via TXT record.
Key reports to watch weekly:
**Domain reputation**: Green (high) = good. Yellow (medium) = warning. Red (low) = you're going to spam. Anything below High needs immediate diagnosis.
**IP reputation**: depends on Lemlist's sending infrastructure but reflects on your domain too.
**Spam rate**: target under 0.1%. Gmail's threshold for trouble is 0.3%. Above 0.5% = severe throttling.
**Authentication**: SPF, DKIM, DMARC pass rates. All should be 99%+.
Set a calendar reminder to review weekly. Catching a reputation drop early gives you time to fix before it cascades.
Step 6
Send a test campaign to a 'seed list' of test inboxes at Gmail, Outlook, Yahoo, ProtonMail. Watch where each lands.
GlockApps (paid, ~$59/mo) is the gold standard. Mail-tester.com (free single-test) is the basic option.
Set up a seed list: 5-10 test inboxes across providers (Gmail, Outlook, Yahoo, AOL, ProtonMail, Hey).
Send a real campaign to the seed list. Wait 5 minutes. Check where each landed: Primary, Promotions, Spam.
Target: Primary inbox at 90%+ of Gmail tests, Outlook 'Inbox' at 80%+, no spam landings.
Run the test before launching every new campaign template. Content drift between campaigns can cause unexpected filter triggers.
Re-run monthly even on stable campaigns — Gmail filter algorithms evolve and what worked last month may degrade.
Common mistakes
Sending from a domain less than 30 days old
What goes wrong: New domains are treated as suspicious by default. Even with perfect DNS, you'll see 40-60% spam-folder rate. Warm-up can\'t overcome domain age in the first month.
How to avoid: Buy sending domains at least 30 days before your first send. Older is better. Aged domains (90+ days with light human activity) have meaningfully better deliverability.
Including images, attachments, or tracked links in cold emails
What goes wrong: Image-heavy cold emails get filtered at 30-50% higher rate than plain text. Tracked links add redirect URLs that look promotional. Attachments are spam-bin material in cold.
How to avoid: First 2-3 emails in a sequence: plain text, no images, no tracked links, no attachments. Add these only after warm-up shows 95%+ placement AND you've validated the specific email template via mail-tester.
Ignoring bounce rates and re-sending to bounced addresses
What goes wrong: Each bounce damages reputation. Sending again to known bounces compounds the damage. ESPs throttle senders with >5% bounce rates aggressively.
How to avoid: Verify lists pre-import. Enable Lemlist's "Auto-pause bounced leads." Audit bounce rate weekly — investigate any campaign over 3%.
Stuffing the same campaign across all your mailboxes simultaneously
What goes wrong: Sudden synchronized volume across 5 mailboxes on the same domain looks like compromise to spam filters. Reputation drops on all mailboxes at once.
How to avoid: Use Lemlist's Inbox Rotation, which staggers sends across mailboxes naturally. Don't run multiple campaigns from the same domain all launching the same hour.
No Google Postmaster Tools monitoring
What goes wrong: You don't know you're in trouble until reply rates have already cratered. By the time symptoms are visible, the damage is 30 days deep.
How to avoid: Set up Postmaster Tools week 1 of any new sending domain. 10 minutes of setup. Weekly 5-minute review. Catches reputation issues before they're catastrophic.
Treating deliverability as a one-time setup
What goes wrong: You configure DNS, run warm-up, launch campaigns. 60 days later, deliverability has silently degraded 20% and you don't notice until pipeline tanks.
How to avoid: Deliverability is ongoing maintenance. Monthly: DNS recheck, postmaster tools review, seed-list test. Quarterly: full audit. This is non-negotiable for sustained outbound.
Recap
Done — what's next
How to set up Lemwarm for domain and inbox warm-up
Read the next tutorial
Hand it off
Deliverability is the most diagnostically-difficult area of outbound — same symptoms, ten possible causes. Specialists carry diagnostic tooling (GlockApps Pro, Postmaster Tools dashboards, blacklist monitors) and patterns from 100+ accounts. An EverestX demand-gen specialist runs deliverability audits in 1-2 hours, ongoing monitoring at $14-16/hr. Typically $200-400/mo for monitoring-only, $600-1,500/mo for full outbound management.
Get a deliverability audit
Check in order: (1) DNS health at mxtoolbox — did SPF/DKIM/DMARC break? (2) Postmaster Tools — did spam rate spike or reputation drop? (3) List quality — did recent imports include junky addresses? (4) Volume — did you spike sends recently? (5) Content — did a new template introduce spam triggers? Don't guess; walk the diagnostic.
No. Even at 20 emails/day, the blast radius if you get flagged is your whole transactional email (invoices, password resets, support). The $12/mo for a separate sending domain is rounding error compared to the recovery cost. Always separate.
30-50 cold emails/day per mailbox is the conservative safe zone. Google's technical limit is 2,000/day but spam filters tolerate far less for cold-pattern sending. Stay conservative and scale via more mailboxes, not more emails per mailbox.
Check at multirbl.valli.org (free, scans 100+ blacklists). If listed at any, request removal per blacklist instructions. Most clear within 24-72 hours. If you're blacklisted at Spamhaus or SORBS, recovery is harder — often easier to retire the domain.
Marginally. A custom tracking domain (track.yourdomain.co) keeps tracking links on your domain rather than Lemlist's default. Slightly better than the default but doesn't fix underlying issues. Worth setting up but won't rescue a damaged domain.
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