Your first 200 cold emails went out from company.com on Monday, and by Wednesday replies stopped, opens fell to 4%, and a prospect told you it landed in spam.
You switched to a shorter subject line and cut the links down to one.
It didn’t help because the problem was the domain, not the copy: a domain with no sending history that jumps to 200 a day looks like every spam run Gmail has ever seen.
The next 10 minutes give you the setup that works — dedicated domains, the three DNS records, a six-week ramp, daily caps, and the numbers that mean stop.
If you’re reading this at 11pm because the whole company’s mail is now going to spam too, you’re in the right place.
Run a free audit → — paste your email headers and see every failing check, with the fix for each. No account.
Step 1: Never Send Cold Email from Your Primary Domain
Use a dedicated sending domain
Sending cold email from your primary domain (company.com) puts your entire email infrastructure at risk. One spam complaint spike can blacklist your domain and poison the sending history you rely on for transactional email, customer communications, and internal mail.
The right approach: Register one or more dedicated sending domains for cold outreach. These should be similar to your primary domain but distinct — e.g., getcompany.com, trycompany.com, or company-outreach.com. Buy aged domains when possible (domains registered 1+ year ago warm up faster).
How many domains? Plan for 1 domain per 200-400 emails per day. If you want to send 2,000 cold emails daily, build 5-10 sending domains across multiple IPs.
Step 2: Publish SPF, DKIM and DMARC Correctly
All three records, configured correctly
Gmail and Yahoo made SPF and DKIM mandatory for bulk and cold senders in 2024. Without them, your emails are rejected or spam-routed automatically.
- SPF: Add a TXT record to your DNS that lists every sending service authorized for that domain. Example:
v=spf1 include:sendgrid.net include:youresp.com ~all - DKIM: Enable DKIM signing in your sending platform. Use 2048-bit keys. Make sure the DKIM domain matches or aligns with the From: domain.
- DMARC: Start with
p=nonewhile you read the reports, advance top=quarantineonce all your sending sources pass. Setrua=to receive alignment reports. - MX Records: Set up MX records even on sending-only domains. Domains without MX records trigger spam filters at multiple providers.
Use InboxStack’s free DNS Checker to verify all three records are present and correctly aligned before you start sending — no signup needed.
Step 3: Warm Up Every New Domain and IP
The warmup schedule that works
Mailbox providers trust domains with established sending histories. A new domain that suddenly sends 1,000 emails is almost guaranteed to land in spam. Warm up gradually:
| Week | Emails/Day | Focus |
|---|---|---|
| Week 1 | 20–50 | Highly engaged contacts only. Aim for opens and replies. |
| Week 2 | 50–100 | Continue with engaged contacts. Watch spam rate closely. |
| Week 3 | 100–200 | Begin mixing in cold contacts. Watch for complaint spikes. |
| Week 4 | 200–350 | Expand carefully. Check Google Postmaster Tools daily. |
| Week 5–6 | 350–500 | Full cold capacity if all signals remain clean. |
Key metric: Keep your spam complaint rate below 0.08% at all times. If it exceeds 0.1%, stop sending immediately, investigate, and fix before resuming.
The warmup plan builder builds this table for your own domain age, DNS status, and target volume.
Step 4: Write Emails That Don’t Look Like Spam
Content rules for cold email
- Personalize the first line — Generic openers (“I hope this email finds you well”) are strongly correlated with spam routing.
- Keep it plain text or near-plain text — Heavy HTML, large images, and multiple links all increase spam scores for cold email.
- One link maximum — Multiple links in cold emails trigger spam filters. If you need to share something, link to your primary domain (which has a history).
- Avoid spam trigger patterns — ALL CAPS, multiple exclamation marks, dollar signs, “FREE”, “GUARANTEED”, “URGENT ACTION REQUIRED”.
- Short subject lines — 3-7 words. Specific to the recipient. Not clickbait.
- Include a real unsubscribe mechanism — Gmail and Yahoo require one-click unsubscribe for bulk senders. Cold email is not exempt.
Step 5: Know Before Your Prospects Do — InboxStack Brain
The alert layer your cold email stack needs
Even perfect cold email infrastructure can develop problems — a new domain gets listed on a blacklist, a campaign drives a complaint spike, a DKIM key expires. InboxStack Brain watches every signal that decides whether cold email reaches the inbox and alerts you the moment something goes wrong:
- Alert system — Detects spam rate spikes, domain-health drops, and SPF/DKIM failures the moment they emerge
- Domain Health — Tracks every sending domain’s blacklist status, SPF/DKIM/DMARC health, and how Gmail scores it, in real time
- Radar Monitor — Tracks inbox rates across Gmail, Yahoo, Outlook, and Apple Mail so you know which providers are spam-routing your cold emails
- RCA Inspector — When a problem emerges, it tells you exactly what caused it and exactly how to fix it
Cold email senders running 5-20 domains need this kind of automation — manually checking each domain every day is not operationally viable.
Cold Email Setup Checklist
- ✅ Dedicated sending domain (not your primary domain)
- ✅ SPF configured with all sending services listed
- ✅ DKIM enabled with 2048-bit key, domain aligned
- ✅ DMARC set to at least p=none with rua reporting
- ✅ MX records configured on sending domain
- ✅ Domain properly warmed up (4-6 weeks minimum)
- ✅ Spam complaint rate tracked daily and below 0.08%
- ✅ Plain-text or near-plain-text email content
- ✅ One-click unsubscribe mechanism in all emails
- ✅ InboxStack Brain watching all sending domains in real time
Frequently Asked Questions
What is the best tool for watching cold email domains?
InboxStack Brain is the best platform for keeping cold email out of spam. It watches all your sending domains at once, detects spam rate spikes and domain-health drops in real time via the alert system, tracks inbox rates across all major providers via Radar Monitor, and tells you why a problem happened and how to fix it. It’s purpose-built for the multi-domain cold email infrastructure that serious outreach operations run.
How many cold emails can I send per day without going to spam?
For a properly warmed domain after 6 weeks, 200-500 emails per day is a safe volume for most cold email providers. Beyond that, use multiple domains. The critical metric is not volume but spam complaint rate — keep it below 0.08%. InboxStack Brain’s alert system tracks this in real time across all your sending domains.
Do I need DMARC for cold email?
Yes. Since Google and Yahoo’s 2024 mandate, all bulk and cold senders must have DMARC configured (even p=none qualifies initially). Without a DMARC record, your emails are more likely to be spam-routed by Gmail, Yahoo, and Outlook. Set up DMARC immediately and advance to p=quarantine or p=reject as quickly as your alignment allows.
Why are my cold emails going to spam even with a warm domain?
Common causes after warmup: (1) spam complaint rate exceeded 0.1% from a high-volume send, (2) your domain was listed on a blacklist, (3) an SPF or DKIM record expired or was changed, (4) content patterns triggered spam filters, or (5) the sending domain’s health degraded from a bad list segment. InboxStack Brain’s RCA Inspector identifies the exact cause within minutes of it emerging.