Master cold email deliverability in 2026. SPF, DKIM, DMARC setup, warm-up schedules, content rules, and monitoring checklist to avoid spam folders.

Why your cold emails land in spam

Deliverability is the #1 problem in B2B cold email. You can write the perfect message — if it lands in spam, nobody reads it.

In 2026, Gmail, Outlook, and Yahoo spam filters are stricter than ever. Google now requires bulk senders to authenticate emails, provide one-click unsubscribe, and stay below spam complaint thresholds. Here are the rules you must follow.

1. Set up SPF, DKIM, and DMARC

This is non-negotiable. Without these three protocols, your emails will be rejected or flagged.

SPF (Sender Policy Framework): Declares which servers can send on behalf of your domain
DKIM (DomainKeys Identified Mail): Cryptographic signature proving the email wasn't tampered with
DMARC: Policy telling receiving servers what to do if SPF/DKIM fail

Quick setup checklist

Protocol	Where to add	Example record
SPF	DNS TXT on root	v=spf1 include:_spf.google.com ~all
DKIM	DNS TXT on selector	Generated by your email provider
DMARC	DNS TXT on _dmarc	v=DMARC1; p=none; rua=mailto:you@domain.com

Test: Send an email to mail-tester.com — aim for 9/10 or higher.

2. Use a separate sending domain

Never send cold emails from your main domain. If your main site is acme.com, create acme-outreach.com or getacme.com for cold email. This protects your main domain's reputation.

3. Warm up your mailboxes

New domains and mailboxes need gradual ramp-up:

Week 1: 5-15 emails/day
Week 2: 15-30 emails/day
Week 3: 30-50 emails/day
Week 4+: Up to 100 emails/day per mailbox

Don't skip this. Sending 200 emails from a brand-new mailbox guarantees spam placement.

4. Check content BEFORE sending

Most tools show you stats after the damage is done. A good deliverability score checks:

Spam trigger words ("free", "limited offer", "click here", "guaranteed")
Email length (ideal: 50-150 words for cold email)
Number of links (0-1 links maximum)
Caps ratio (no SHOUTING IN ALL CAPS)
Image-to-text ratio (plain text is best for cold email)

HeraMail calculates a 0-100 deliverability score on every email before you send it.

5. Personalize every email

First name
Company name
Industry or role reference
A specific observation about their business

AI can help personalize at scale, but the result must read like a human wrote it.

6. Keep emails short

Ideal cold email: 3-5 sentences, 50-125 words. Emails over 200 words see significantly lower reply rates.

Hook (1 sentence) — context or question
Value (1-2 sentences) — what you offer
CTA (1 sentence) — clear, simple ask

7. Skip images and complex HTML

Cold emails should look like personal emails. No banners, no logos in the body, no complex formatting. Plain text with a simple signature gets the best deliverability.

8. Include an unsubscribe link

Since February 2024, Gmail and Yahoo require an unsubscribe mechanism for bulk senders. This is also a GDPR/CAN-SPAM requirement. A discreet unsubscribe link doesn't hurt reply rates but protects your sender reputation.

9. Clean your list regularly

Hard bounce (address doesn't exist): Remove immediately
Soft bounce (full mailbox, temporary error): Retry 1-2 times, then remove

Aim for a bounce rate below 2%.

10. Use multi-inbox rotation

Load is distributed
If one mailbox is throttled, others take over
Daily volume increases without increasing per-mailbox risk

Monitoring checklist

[ ] SPF, DKIM, DMARC all passing (check mail-tester.com)
[ ] Sending domain separate from main domain
[ ] Mailboxes warmed up for 2+ weeks
[ ] Deliverability score 80+ on every email
[ ] Bounce rate below 2%
[ ] Spam complaint rate below 0.1%
[ ] Unsubscribe link in every email

Try HeraMail free — deliverability score on every email, before you send: heramail.io

Cold Email Deliverability Guide 2026: Land in the Inbox