What is email list hygiene and why does it affect deliverability?

List hygiene is the ongoing practice of removing addresses from your sending list that are dead, invalid or disengaged, so you only email people who can and want to receive it:

• Remove hard bounces - addresses that reject permanently should be dropped immediately; repeatedly emailing them signals a careless sender.
• Prune the disengaged - people who have not opened anything in 6 to 12 months drag down your engagement metrics and often become complaints.
• Never buy or scrape lists - purchased addresses are the fastest route to spam traps and complaints.
• Validate at signup - a confirmation step keeps typos and fake addresses off the list in the first place.

A smaller list of engaged recipients outperforms a big stale one - clean it regularly, not just when deliverability drops.