Why does list hygiene matter for deliverability?

Mailbox providers judge senders by the quality of their audience. When you send to dead addresses, abandoned inboxes, spamtraps, or fake signups, you show mailbox providers that you do not understand who you are sending to. That signal lowers your domain reputation and IP reputation, which pushes more of your messages to spam. Reputation damage accelerates once hard bounce rates exceed two percent or complaint rates exceed zero point one percent. These thresholds are the red lines for most providers.