Email Deliverability: Why Your Cold Emails Land in Spam (and How to Fix It)
Email deliverability for B2B outbound: SPF, DKIM, DMARC, domain warming, sending infrastructure, and the most common mistakes that send your emails to spam.
Email deliverability: the basics
Deliverability decides whether your email lands in the inbox or in the spam folder. For cold email it’s even more critical than for a newsletter — because the recipient doesn’t know you and isn’t waiting for your email.
The deliverability chain:
Your email → Sending server → Internet → Recipient server → Spam filter → Inbox
↓
SPF check
DKIM check
DMARC check
Content check
Reputation check
↓
Inbox or spam?The technical foundation: SPF, DKIM, DMARC
SPF (Sender Policy Framework)
What: Defines which servers are allowed to send emails for your domain. How: DNS TXT record on your domain. Without SPF: Email providers suspect spoofing → spam.
DKIM (DomainKeys Identified Mail)
What: A digital signature that proves the email wasn’t tampered with. How: DNS TXT record + signing by the email server. Without DKIM: The email can’t be verified as authentic → spam risk.
DMARC (Domain-based Message Authentication)
What: Tells the recipient server what to do if SPF/DKIM fail.
How: DNS TXT record with a policy (none, quarantine, reject).
Recommendation: Start with p=none (monitoring only), then move up to p=quarantine.
All three are mandatory. Without SPF+DKIM+DMARC you have almost no chance of reaching the inbox in B2B outbound.
Domain warming: the process
Why warming is necessary
A new domain has no reputation. Email providers don’t know it. Sending 100 emails/day right away = getting flagged as spam immediately.
The warmup plan
| Week | Emails/day | Type |
|---|---|---|
| 1 | 5-10 | Warmup only (simulated conversations) |
| 2 | 15-25 | Warmup + first real emails (5-10) |
| 3 | 30-40 | 50/50 warmup and real emails |
| 4 | 40-50 | Mostly real emails, warmup continues |
Warmup tools
Most outbound tools have built-in warmup:
- Instantly: warmup network with thousands of accounts
- Lemlist: lemwarm feature
- Warmup Inbox: standalone tool
Important: Never stop warmup completely — even after ramp-up, keep sending 10-20% warmup emails.
Sending infrastructure
Separate domains (mandatory)
- Main domain: company.com → regular business communication only
- Sending domain 1: company-mail.com → outbound emails
- Sending domain 2: get-company.com → backup/rotation
- Sending domain 3: company-team.com → additional sender
Mailboxes per domain
- 2-3 mailboxes per sending domain
- Each mailbox: max 30-50 emails/day
- Rotate between mailboxes
Example setup for 100 emails/day
company-mail.com
├── max@company-mail.com (30 emails/day)
├── sarah@company-mail.com (30 emails/day)
└── team@company-mail.com (20 emails/day)
get-company.com
└── max@get-company.com (20 emails/day as backup)Content rules for good deliverability
Avoid
- Spam-trigger words: “free”, “offer”, “today only”, “guarantee”
- Too many links (max 1-2 per email)
- Images in cold emails (plain text performs better)
- HTML formatting (bold, colors, buttons)
- Large attachments
- ALL CAPS in the subject line
- Too many recipients in CC/BCC
Best practices
- Plain-text emails (like a real 1-to-1 message)
- Short (80-120 words)
- Personal sender address (firstname@domain)
- Max 1 link
- Natural language (no marketing speak)
- Unsubscribe option in the copy
Monitoring
Metrics to track
| Metric | Good | Warning | Critical |
|---|---|---|---|
| Open rate | >50% | 30-50% | <30% |
| Bounce rate | <2% | 2-5% | >5% |
| Spam complaints | <0.1% | 0.1-0.3% | >0.3% |
| Unsubscribe rate | <1% | 1-3% | >3% |
When there’s a problem
- Open rate drops: check SPF/DKIM/DMARC, review content
- Bounce rate rises: verify the email list, remove old addresses
- Spam complaints: rework content, reduce volume, intensify warmup
- Domain blocked: set up a new sending domain, pause the old one
Conclusion
Email deliverability is the basic prerequisite for any cold email campaign. Without SPF/DKIM/DMARC, domain warming, and separate sending domains, your emails land in spam — no matter how good the content is. Invest 2-3 weeks in the setup before launching your first campaign. It’s the difference between a 50% and a 5% open rate.
Common questions
Why do my cold emails land in spam?
The most common reasons: missing or incorrect SPF/DKIM/DMARC records, a new domain without warmup, too much volume per sender, spam-trigger words in the copy, too many links/images, a high bounce rate, and no unsubscribe option. Usually it's a combination.
What is email warmup?
Email warmup is the process of slowly building up a new email domain/address. Instead of immediately sending 100 emails/day, you start with 5-10 and ramp up over 2-4 weeks. Warmup tools (built into Instantly, Lemlist) also simulate real conversations to build reputation.
What are SPF, DKIM, and DMARC?
SPF verifies that the sending server is authorized to send on behalf of your domain. DKIM cryptographically signs emails. DMARC defines what happens if SPF/DKIM fail. Together, all three tell email providers: 'This email is genuine, not spoofed.' Without them, emails frequently land in spam.
Should I use my main domain for cold emails?
No, never. Use separate sending domains (e.g. company-mail.com instead of company.com). If a sending domain gets damaged by spam reports, your main domain — and with it your regular business communication — stays protected.