What’s a broken URL and why does it matter?
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You send an email with a link to your latest blog post. A subscriber clicks. Instead of seeing your content, they hit a 404 error page. That's a broken URL, and it's worse than just a frustrating user experience.
Spam filters actively test links before your email even reaches the inbox. They're looking for patterns: dead endpoints suggesting abandoned campaigns, suspicious redirects that hide the final destination, domains on known blocklists, and newly registered domains with no reputation history. If filters encounter a broken link, they see incompetence or deception. Either way, it's a deliverability signal that hurts your sender score.
The damage multiplies. You lose the click-through (missed conversion). You damage your brand's credibility. And you increase the likelihood that future emails get filtered. This is especially risky with dynamic URLs built from personalization or conditional logic. A broken link in one variation could fail silently for certain audience segments.
Protect yourself with pre-send testing. Most ESPs offer link checking built into campaign review. Test every link manually before sending, or use automated tools that catch common mistakes. Pay special attention to URLs with personalization variables, affiliate links, or tracking parameters. Testing email links before send is non-negotiable, and it's worth building into your workflow. Use Review My Emails Email Header Analyzer to spot link issues in your headers, or test your designs directly with our Subject Line Tester tool.
Related: spam filters, subject line.
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