Avoiding the Most Overlooked DNS Mistakes in Cold Email

Cold email is still one of the most effective channels for startups and sales teams looking to drive growth, book meetings, and build new relationships. But the reality is, no matter how compelling your messaging or how targeted your list, your campaigns simply won’t perform if you ignore the technical side, especially DNS records and email authentication.
DNS mistakes are the “silent killers” of cold email outreach. They’re easy to overlook, but the consequences are severe: plummeting deliverability, damaged sender reputation, and a reply rate that flatlines. In this guide, we’ll break down the most common DNS mistakes, why they matter, and how you can fix them to ensure your emails reach the inbox, not the spam folder.
Whether you’re a founder running your own outreach or a sales manager scaling a team, this best practices guide will help you avoid the DNS pitfalls that quietly undermine even the best cold email strategies.

Why DNS and Email Authentication Are Critical for Cold Email

What is DNS and Why Does It Matter?

DNS (Domain Name System) is like the phone book of the internet. It tells email servers where to find your domain and how to handle your emails. When you send cold emails, inbox providers (like Gmail, Outlook, and Yahoo) check your DNS records to verify that you are who you say you are.

Email Authentication: Your Reputation on the Line

There are three main types of DNS records that play a crucial role in email authentication:

1. SPF (Sender Policy Framework): Specifies which mail servers are allowed to send email on behalf of your domain.
2. DKIM (DomainKeys Identified Mail): Adds a digital signature to your emails, proving they haven’t been altered in transit.
3. DMARC (Domain-based Message Authentication, Reporting, and Conformance): Tells receiving servers what to do if an email fails SPF or DKIM checks.

If these records are missing or misconfigured, your emails are more likely to be flagged as spam or rejected entirely. Worse, your domain could be used for phishing or spoofing attacks, further damaging your reputation.

The Most Overlooked DNS Mistakes and How to Fix Them

1. Missing or Incorrect SPF Records

What’s the Problem?
SPF records are your first line of defense. Without them, anyone can send emails claiming to be from your domain. But even minor errors, like a missing IP address or a syntax mistake, can cause your emails to fail authentication.

Common Mistakes:

• Not publishing an SPF record at all
• Typos or syntax errors in the SPF record (e.g., missing spaces, incorrect use of “include:”)
• Exceeding the 10 DNS lookup limit (a common issue as your tech stack grows)
• Forgetting to update your SPF record when adding new tools (like CRMs or marketing automation platforms)

Real-World Example:
A SaaS startup adds a new outreach tool but forgets to update its SPF record. Suddenly, prospecting emails start bouncing or landing in spam, and reply rates drop by 40%.

How to Fix It:

• Use an SPF record generator to avoid syntax errors.
• After every change (like adding a new sending tool), update your SPF record and test it with online tools.
• Keep your SPF record as simple as possible, and remove old or unused includes.
• Regularly audit your SPF record to ensure you haven’t hit the 10-lookup limit.

2. Absent or Misconfigured DKIM Records

What’s the Problem?
DKIM adds a layer of trust by attaching a digital signature to every email. If your DKIM record is missing or set up incorrectly, your emails can be easily forged or flagged as suspicious.

Common Mistakes:

• Failing to publish a DKIM record at all
• Using the wrong selector (the “name” part of the DKIM record)
• Publishing the public key in the wrong DNS field (should be a TXT record)
• Not enabling DKIM on all sending domains and subdomains

Real-World Example:
A sales team launches a campaign from a new subdomain but forgets to set up DKIM. Their emails pass SPF but fail DKIM, leading to poor inbox placement and a spike in spam complaints.

How to Fix It:

• Enable DKIM in your email platform’s settings.
• Publish the DKIM public key as a TXT record in your DNS.
• Use online DKIM validators to check that the signature is valid.
• Set up DKIM for every domain and subdomain you use to send cold emails.

3. No DMARC Policy or Weak DMARC Settings

What’s the Problem?
DMARC tells inbox providers what to do if an email fails SPF or DKIM checks. Without it, you have no control over how unauthenticated emails are handled, leaving your domain vulnerable to spoofing.

Common Mistakes:

• Not publishing a DMARC record at all
• Setting DMARC policy to “none” and never updating it
• Not monitoring DMARC reports (so you never spot issues)
• Using an overly strict policy before SPF/DKIM is properly set up (leading to false positives)

Real-World Example:
A tech company sets DMARC to “reject” before verifying that all their legitimate tools are passing SPF and DKIM. Suddenly, critical emails (like invoices and support tickets) bounce or disappear.

How to Fix It:

• Start with a DMARC policy of “none” to collect reports.
• Monitor DMARC reports for at least a few weeks to spot issues.
• Gradually move to “quarantine” or “reject” as you gain confidence in your setup.
• Use a DMARC monitoring tool to automate report collection and analysis.

4. Forgetting About Subdomains

What’s the Problem?
Many organizations only set up SPF, DKIM, and DMARC for their root domain (e.g., yourcompany.com) but forget about subdomains (e.g., mail.yourcompany.com, sales.yourcompany.com). Attackers can exploit these gaps.

Common Mistakes:

• Not authenticating all sending subdomains
• Assuming root domain policies cover subdomains (they don’t, unless explicitly configured)
• Using subdomains for campaigns without proper DNS setup

Real-World Example:
A lead gen agency launches a campaign from outreach.yourcompany.com. Without SPF/DKIM/DMARC on the subdomain, their emails are easily spoofed, and deliverability tanks.

How to Fix It:

• Identify all domains and subdomains used for sending email.
• Set up SPF, DKIM, and DMARC for each.
• Use “sp” (subdomain policy) tag in your DMARC record to control subdomain behavior.

5. Overlooking DNS Propagation Delays

What’s the Problem?
Changes to DNS records don’t take effect instantly. It can take anywhere from a few minutes to 48 hours for updates to propagate globally. Sending emails before your changes are live can cause authentication failures.

Common Mistakes:

• Launching campaigns immediately after updating DNS
• Not verifying DNS changes with online tools
• Assuming all recipients’ servers see your updates instantly

Real-World Example:
A startup updates its DKIM record and sends a major cold email campaign the same afternoon. Half the recipients’ servers haven’t seen the new record yet, so emails fail DKIM and land in spam.

How to Fix It:

• Make DNS updates well before major campaigns.
• Use DNS propagation checkers to confirm changes are live.
• Test email authentication from multiple locations before launching.

Pro Tips and Actionable Steps for Startups and Sales Teams

1. Regularly Audit Your DNS Records:
   Use free tools like MXToolbox, Google Admin Toolbox, or DMARC Analyzer to check your SPF, DKIM, and DMARC records.
2. Document Every Change:
   Keep a simple change log (even a Google Doc) of every DNS update, who made it, and why.
3. Coordinate With IT or Your Domain Admin:
   Don’t make DNS changes in isolation; loop in whoever manages your domain to avoid accidental misconfigurations.
4. Test, Test, Test:
   After any change, send test emails to multiple providers (Gmail, Outlook, Yahoo) and check where they land.
5. Monitor Deliverability Metrics:
   Watch for sudden drops in open or reply rates; these often signal DNS or authentication issues.
6. Automate Where Possible:
   Use platforms like Mailpool that offer automated deliverability setup, ongoing monitoring, and proactive alerts for DNS/authentication issues

Troubleshooting Checklist: Diagnosing and Fixing DNS Issues

• Are SPF, DKIM, and DMARC records published for every sending domain and subdomain?
• Do your SPF records include all legitimate sending services and stay under the 10-lookup limit?
• Are DKIM signatures valid and matching the correct selector for each tool?
• Is your DMARC policy set appropriately for your current authentication confidence?
• Have you verified that DNS changes have propagated before launching new campaigns?
• Do you monitor DMARC reports to catch spoofing or authentication failures?
• Is your team aware of all domains/subdomains used for outbound email?

Conclusion

DNS mistakes are often invisible until it’s too late, when your cold email campaigns underperform, your sender reputation takes a hit, or your domain gets blacklisted. But with a proactive approach, you can avoid these common pitfalls and give your outreach the best possible chance of success.
By ensuring your SPF, DKIM, and DMARC records are set up correctly (for every domain and subdomain), monitoring deliverability, and leveraging automation tools, you’ll boost inbox placement, protect your reputation, and see better results from every campaign.
Ready to leave DNS headaches behind? Sign up with Mailpool and let our automated deliverability setup and DNS management keep your emails landing where they belong: the inbox.