How do you measure list quality?

List quality isn't one number. It's a handful of signals you read together. The good news: most of them come straight from your ESP's dashboard. The bad news: a lot of senders only look when something's already wrong.

Here are the metrics that actually matter, and what counts as healthy:

• Hard bounce rate: Should be under 2% per send. Above that, you've got addresses that no longer exist (or never did) and mailbox providers are noticing. Clean these immediately.
• Spam complaint rate: Should stay under 0.1%. Google Postmaster Tools gives you this for Gmail traffic directly. Above 0.3% and you're in danger territory with Gmail's bulk sender requirements.
• Unsubscribe rate: Under 0.5% per send is a reasonable benchmark. Spikes tell you something about a specific campaign or segment, not just the list.
• Engagement rate: Opens and clicks from people who actually read your emails, not just the list count. A 10,000-person list where 8,000 haven't opened in six months is a low-quality list.
• Opt-in recency: How fresh are these addresses? A list from five years ago has probably lost 30-50% of its deliverable contacts to account churn. Newer opt-ins perform better.

Beyond these, you can check validation status. If you run your list through a validation tool, you'll see how many addresses have MX record problems, how many are catch-alls (the server accepts everything but might bounce later), and whether any disposable domains slipped through. List hygiene is the ongoing work of keeping these numbers in range.

The simplest quality check you can do right now: filter your list to subscribers who haven't clicked in 90 days and look at that percentage. If it's over 50%, you've got a quality problem and a deliverability risk waiting to surface.

Want to know where your list stands? Our list cleaning service flags every category of problem address and gives you a detailed breakdown. Or if you'd rather troubleshoot your own numbers, reach out and we'll take a look.