Email List Hygiene: Bounce Rate vs Spam Complaints, and Which to Fix First

Bounces and spam complaints are the two numbers that tell you most about the health of a list, and they're often lumped together. They measure different failures. One says you're mailing people who don't exist. The other says you're mailing people who don't want it.

Bounce rate: addresses that don't work

A hard bounce is a permanent failure, usually an address that doesn't exist. A soft bounce is temporary, such as a full mailbox or a throttled connection. The number to watch is the hard bounce rate, and the commonly cited ceiling is about 2%. Past that, providers read your list as collected carelessly.

• Causes: typos, old or scraped data, people who left their company, purchased lists
• Fix: verify addresses before sending, suppress every hard bounce immediately, and never retry one
• It's the faster problem to solve, because the cause is entirely on your side and fully measurable

Spam complaints: people who say no

A complaint is a recipient pressing the spam button. Gmail and Yahoo ask bulk senders to stay under 0.3% and aim for under 0.1%. It matters more than any bounce rate because it's a direct statement from a person, and providers weight it that way.

• Causes: mail nobody asked for, mail that's irrelevant, mail that arrives too often, and an unsubscribe link that's hard to find
• Fix: send only to people with a reason to expect it, make unsubscribing a single obvious step, and honour it immediately
• You can't verify your way out of it. Verification catches dead addresses, not unwanted mail

Which comes first

If both are high, fix bounces first since it's mechanical and quick, and the damage compounds if you keep mailing dead addresses. Then work on complaints, which take longer because they depend on targeting and message, not on data cleaning. If only complaints are high on a clean list, no amount of cleaning will help: change who you send to and what you send.

A routine that works

• Verify every new list before the first send, and re-verify old ones before you re-use them
• Suppress hard bounces and complaints automatically, across every tool you use, so nobody gets re-imported
• Retire addresses that haven't engaged for six to twelve months, or ask them to confirm before mailing again
• Remove role accounts such as info@ and support@ from cold lists
• Watch the rates per campaign and per domain, because a single bad list can hide inside a healthy average

Verify a list for syntax, dead domains, disposable and role addresses

Understand how complaints reach you through feedback loops

What spam traps are and how lists collect them

Bounces tell you the list is wrong. Complaints tell you the message is. Fix the one that's measurable first.