Your campaign was running fine. You were getting 8-12% reply rates, booking calls, closing deals. Then something shifted. Reply rates dropped to 2-3%. Opens flatlined. Everything that worked last month feels broken now.
The worst part? You don't know what changed.
Cold email campaigns don't just die for one reason. There are usually three or four moving pieces breaking at the same time - and most people only look at one. Here's what's actually happening, and how to diagnose it.
Your Domain Reputation Just Got Hit
This is the most common culprit, and the hardest to see coming.
Every email you send affects your domain's reputation with the major inbox providers - Gmail, Outlook, Yahoo. This reputation score is based on bounce rates, complaint rates, spam trap hits, and authentication failures. When your score drops below a certain threshold, your emails start landing in spam or getting rejected entirely.
Here's the problem: you don't see this happening in real time. Your campaign looks fine in your email tool. Then suddenly, your open rate is cut in half and you have no idea why.
Three specific things cause domain reputation collapse:
- Bounce rate over 5% - If more than 5% of your emails are bouncing, you're sending to bad addresses. This happens when your list quality drops or you're not validating emails before sending. Check your bounce rate in your email provider's dashboard. If it's above 5%, pause the campaign and clean your list.
- Spam trap hits - These are honeypot email addresses that ISPs use to catch senders with poor list hygiene. If you're buying lists, scraping emails, or not removing unengaged subscribers regularly, you'll hit them. One spam trap hit can tank your domain for weeks. If this happens, you need to investigate whether your domain got blacklisted and consider switching to a new sending domain entirely.
- No authentication or weak authentication - SPF, DKIM, and DMARC aren't optional. If these aren't set up correctly, email providers will treat your mail as suspicious. Check your email provider's authentication settings. All three should show as