How do bounces affect deliverability metrics?

You send a campaign, and a chunk of your list bounces back. It feels like a minor nuisance. But ISPs are watching, and those bounces are telling a story you might not want told.

At the most basic level, a high bounce rate signals that you're not taking care of your list. ISPs read that as a sign you're emailing addresses you haven't earned permission from, or that you've let your list go stale. Either way, your sender reputation takes a hit.

Here's roughly what that looks like in practice. A hard bounce rate above 2% starts raising flags. Above 5% and your ESP may put your account under review. Hit 10% and suspension becomes very real. These aren't rigid industry-wide rules (every ESP sets its own thresholds), but they're a solid mental model to work with.

The ISP response typically escalates in stages. First they slow down how many of your messages they accept (throttling). Then they start sending more of your mail to spam. If the problem persists, they block you temporarily. Repeated offenses can get you blocked for good.

What makes this tricky is that bounce history doesn't reset overnight. The damage can follow your domain for months. Recovery is possible, but it takes time and consistently clean sending behavior. Prevention is always the easier path (of course, easier said than done, but still).

The practical takeaway is that hard bounces need to be suppressed immediately. Soft bounces that repeat across multiple sends should be treated with the same urgency. Don't let them pile up hoping they'll fix themselves.

If your bounce rate is already climbing, cleaning your list is the most direct fix. You can run your list through RME Clean to catch invalid addresses, spam traps, and addresses that are likely to cause problems before you send again. It's a lot cheaper than rebuilding a damaged sender reputation from scratch.