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A dirty list is the single biggest hidden killer of deliverability. Inbox providers don't judge you on list size — they judge you on how the people on your list actually behave. A smaller, engaged list will always outperform a bloated, ignored one.
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Roughly 22-28% of any email list decays — goes invalid, changes jobs, abandons the inbox — within a single year. Every one of those dead addresses sitting on your list is a landmine: it either bounces (hurting your sender score) or sits there never opening (dragging down your engagement rate, which inbox providers read as a signal that your content isn't wanted).
You cannot buy your way out of this with volume. Delivery rates above 95% and strong inbox placement only happen once invalid and dead addresses are removed.
| Type | What it is | What to do |
|---|---|---|
| Hard bounce | Address doesn't exist — typo, deactivated account, invalid domain | Suppress immediately and permanently |
| Soft bounce | Temporary issue — full inbox, server timeout | Suppress after 4+ consecutive soft bounces |
| Unengaged | Valid, real person, but hasn't opened/clicked in months | Run through the sunset process below before suppressing |
Hard bounce suppression:
Soft bounce suppression: