3 Infrastructure Mistakes That Put You on the ISP Naughty List

If your emails keep landing in spam, there’s a good chance it’s not your content but your infrastructure that’s causing the problem. Internet Service Providers (ISPs) are increasingly strict about who gets to enter the inbox. One wrong move in your setup, and you could end up on their “naughty list” losing valuable reach, credibility, and potential revenue.

In this blog, we’ll uncover three common infrastructure mistakes that can wreck your deliverability and show you how to avoid them.

1. Misconfigured SPF, DKIM, and DMARC Records

Think of SPF, DKIM, and DMARC as your sender ID cards. They prove to ISPs that your emails are legitimate and not forged by spammers.

• SPF (Sender Policy Framework) tells the receiving server which IP addresses are allowed to send emails on your domain’s behalf.
• DKIM (DomainKeys Identified Mail) adds a digital signature to your emails, verifying they haven’t been altered in transit.
• DMARC (Domain-based Message Authentication, Reporting, and Conformance) ties SPF and DKIM together and gives instructions on what to do if an email fails authentication.

The mistake: Many businesses set these records incorrectly, have multiple conflicting SPF entries, or skip DMARC entirely. This creates red flags for ISPs, making your domain look untrustworthy.

The fix: Perform a DNS check to ensure your SPF, DKIM, and DMARC records are correctly configured and aligned. Use reliable tools to validate your settings, and update them whenever your email-sending infrastructure changes.

2. Using a Shared Sending Environment With Poor IP Reputation

Even if your domain is clean, sending emails through a shared server or IP with “bad neighbors” can tank your reputation. ISPs often block or filter all emails coming from an IP address if one sender is flagged for spam.

The mistake: Using low-cost email services that don’t separate you from other senders. You might be unknowingly tied to senders blasting spam or violating compliance rules.

The fix: Use a dedicated sending domain and IP address for your campaigns. This gives you complete control over your reputation and ensures no one else’s bad practices affect your deliverability.

3. Ignoring Reverse DNS and rDNS Matching

Reverse DNS (rDNS) is like a phonebook lookup for your mail server. It tells receiving servers that the IP address sending the email matches your domain name.

The mistake: Many businesses overlook setting up reverse DNS, leaving ISPs unsure about the legitimacy of their sending infrastructure. This can lead to spam filtering or outright blocking.

The fix: Work with your hosting or email service provider to configure reverse DNS correctly. Make sure your rDNS record matches the domain you’re sending from to maintain trust with ISPs.

Your sending infrastructure is the backbone of email deliverability. Even with the best content, if your SPF/DKIM/DMARC are misconfigured, you’re sharing IP space with bad actors, or your reverse DNS is broken, ISPs won’t hesitate to block you.

By auditing and fixing these technical missteps, you’ll protect your domain’s reputation, stay off the ISP naughty list, and ensure your emails land where they belong the inbox.