What’s the risk of over-validation?

Validation tools are powerful, but they can also be a bit trigger-happy. If you validate a large, older list without any safeguards, you might suppress addresses that belong to real people who genuinely want your emails. That's the risk of over-validation, and it's worth thinking through before you hit clean.

The false positive rate varies depending on which tool you use and what's in your list. Most reputable validators sit somewhere between 2% and 8% false positives on an average B2B or mixed list. On lists with a high proportion of catch-all domains, that number can climb higher, because the tool genuinely can't tell if the address is real without sending to it. Corporate domains, university addresses, and anything behind aggressive firewalls tend to trigger the most false flags.

Here's what causes the problem:

• Catch-all domains accept every email at the SMTP level, so validators mark them as "unknown" or risky rather than valid. That bucket can include lots of real people.
• Anti-spam firewalls at some companies actively block SMTP pings, making valid addresses look unreachable.
• Temporary server issues during validation can flip an address to invalid just because the receiving server was down at that moment.
• Aggressive toxicity scoring can flag legitimate addresses from shared domains that happen to have a bad reputation history.

So what do you actually do about it? The safest approach is to treat validation results as a starting point, not a final verdict.

A practical rollout looks like this:

1. Never auto-delete. Suppression is your friend. Move risky addresses to a suppression segment rather than deleting them entirely. You can always revisit.
2. Protect your engaged subscribers first. If someone opened or clicked in the last 90 days, keep them regardless of what the validator says. Recent engagement is stronger evidence of a real address than any tool score.
3. Treat the "unknown" and "catch-all" buckets separately. These aren't the same as hard invalids. Consider sending a light re-engagement email to that segment and watching what happens before you suppress.
4. Start with the oldest, coldest part of your list. Validate in stages, beginning with addresses that haven't engaged in 12 or more months. Lower stakes, cleaner signal.
5. Run a small test first. If your list is 100,000 addresses, validate 5,000 from a representative slice, then compare results against what you know about that group before going full scale.

Validation is a tool that informs your judgment. It's not a replacement for it. A real subscriber working behind a corporate firewall at a company with a catch-all domain might look risky on paper, but their engagement history will tell you the truth.

If you want a human to look at your results before you make big suppression decisions, our SOS hotline is free. Or if you want to run a clean and see exactly what lands in each bucket, RME Clean gives you a full breakdown with labels so you're never flying blind.