Sending Cold Emails? Here’s How to Avoid the Blacklist

Cold email works — when it’s done right.

But too many founders, sales teams, and marketers rush into it with one domain, one inbox, and zero warm-up... only to watch their emails land in spam, bounce, or worse — get blacklisted.

If you're serious about using cold outreach to grow your pipeline, your infrastructure matters as much as your message. In this edition of GTM Guild, we’ll show you how to set up cold email infrastructure the right way — clean, compliant, and optimized for deliverability.

Why Infrastructure Matters in Cold Outreach

You could write the most relevant, personalized cold email ever. But if your email gets filtered, flagged, or blocked — no one sees it.

Cold email isn’t just about copy. It’s a technical game too.
Think of your infrastructure like a digital reputation system. If it’s set up poorly, email providers will treat you like spam.

If it's clean, validated, and properly warmed up — you're in business.

Step 1: Don’t Use Your Primary Domain

Golden Rule: Never send cold emails from your main business domain (e.g., yourstartup.com).

Why? Because if something goes wrong — spam complaints, blacklisting, or domain reputation drops — you don’t want to risk transactional emails, investor comms, or customer support being affected.

What to do instead:

• Register a lookalike domain: yourstartup.co, getyourstartup.com, or yourstartup.io

• Use up to 2–3 variations to rotate across campaigns and avoid volume-based penalties

Step 2: Set Up DNS Records Properly

Email authentication is non-negotiable. Without these records, your emails will likely go to spam — or not get delivered at all.

You’ll need to set up the following in your domain’s DNS settings:

• SPF (Sender Policy Framework): Tells email providers which servers can send mail on your behalf

• DKIM (DomainKeys Identified Mail): Adds a digital signature to validate that the message wasn’t altered

• DMARC (Domain-based Message Authentication, Reporting & Conformance): Gives inboxes rules on what to do if SPF/DKIM fail

• Custom Tracking Domain (optional but ideal): Masks link-tracking URLs (e.g., from tools like Instantly, Smartlead, Mailshake)

Use free tools like MxToolbox or MailTester to check if everything is working correctly.

Step 3: Set Up Dedicated Inboxes

Create separate inboxes for outreach. For example:

• [email protected]

• [email protected]

• [email protected]

This lets you spread volume, test different angles, and isolate deliverability issues.

Most cold outreach platforms support multiple inboxes for sending rotation — take advantage of it.

Step 4: Warm Up Your Inbox — Don’t Skip This

This is where most people go wrong.

Cold email isn’t just cold to your prospect — your inbox is also cold to email providers. Sending 50 messages on day one from a new inbox is a red flag.

How to warm up properly:

• Use automated warm-up tools like Mailwarm, Instantly Warmup, or Smartlead’s built-in options

• These tools simulate replies, opens, and gradual volume increase across a network of inboxes

• Run warmup for at least 2–3 weeks before starting real outreach

• Maintain a steady volume, even after launch

This builds sender reputation organically.

Step 5: Limit Daily Sending Volume

Even after warm-up, you don’t want to blast hundreds of emails at once.

Best practice:

• Start with 20–30 emails per inbox per day

• Scale gradually by 10–20% every few days

• Cap around 50–100 max per inbox per day (depending on reply/complaint rates)

Use sending windows (e.g., 9am–5pm) and randomized sending intervals to mimic human behavior.

Step 6: Monitor Deliverability and Replies

Pay close attention to:

• Open rates: If it drops below 30%, check your spam score

• Bounce rates: Should stay under 5% (validate all leads beforehand)

• Reply rates: Signals engagement and relevance

• Spam reports: Too many = reputation tanked

Tools like Smartlead, Instantly, or Lemwarm have built-in dashboards to track performance and warnings.

Bonus: Comply With Global Regulations

Cold outreach is legal in many regions — but compliance matters:

• Include an opt-out option (even in plain text)

• Avoid misleading subject lines

• Don’t pretend you know the person if you don’t

• Respect do-not-contact requests immediately

Falling foul of laws like GDPR, CAN-SPAM, or PECR can get you fined — or worse, permanently blacklisted.

Final Thoughts:

Most cold email failures have nothing to do with messaging — and everything to do with poor infrastructure.

If you're treating cold email like a growth channel, treat the technical setup with the same care as you would product or code. Think long-term, build reputation slowly, and protect your domain like a brand asset.

Because in cold outreach, deliverability is everything. If your emails don’t land, nothing else matters.

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Until next time,
– The GTM Guild Team