Email list decay is the gradual loss of valid, reachable, interested contacts on a mailing list, even when nobody unsubscribes. Addresses die when people change jobs, abandon personal inboxes, or switch providers, and live addresses go quiet when people lose interest. Every list decays; the only question is how fast yours does and whether you remove the bad addresses before they cause bounces and complaints.

This post explains where decay comes from, what the primary data can and can’t tell you, and how to measure decay on your own list instead of trusting a generic statistic.

What email list decay actually means

People use “list decay” for two different things, and it helps to separate them:

Technical decay. The address no longer accepts mail. Sending to it produces a hard bounce.
Engagement decay. The address still works, but the person stopped reading. Sending to it produces silence, and occasionally a spam complaint.

Technical decay is easier to see because bounces are reported back to you. Engagement decay is harder to see but often larger, and it affects deliverability through low engagement and complaints.

There’s also a third, less obvious outcome: an address that died and then came back as something else. Some mailbox providers and anti-spam groups turn long-abandoned addresses into recycled spam traps. AWS describes a spam trap as a dormant email address used exclusively to lure unsolicited email, and notes that hitting them usually points to a problem with how addresses are acquired or maintained. For how traps end up on real lists, see spam traps: the two kinds and how they got on your list.

Why email lists decay: the main causes

People change jobs

For B2B lists, this is the largest driver of technical decay. When someone leaves a company, their work address is typically disabled.

The U.S. Bureau of Labor Statistics measures how long people stay with an employer. In its Employee Tenure release published September 24, 2026, BLS reported median tenure with the current employer of 4.1 years in January 2026, up from 3.9 years in January 2024. The same release put the share of workers who had been with their employer for a year or less at 20.6 percent.

Those figures don’t translate directly into an email decay rate. Not every job change kills an address (some companies forward mail for a while), and your list may skew toward more or less mobile roles. But they make the point: a meaningful share of the workforce turns over every year, and each move can take a work address with it. A B2B list you haven’t touched in a year has certainly lost some contacts.

Personal inboxes get abandoned

Consumers sign up for newsletters with an address, then drift to a new one. Providers eventually clean up those dead accounts:

Google said in May 2023 that it may delete a personal Google Account that has not been used or signed into for at least 2 years, with deletions beginning no earlier than December 2023.
Yahoo says a Yahoo Mail mailbox that hasn’t been accessed for 12 months becomes inactive, stops receiving new email, and has its contents permanently deleted.

So an address that was valid when someone signed up three years ago may now bounce, simply because its owner moved on and the provider tidied up.

Domains expire and companies change

Startups shut down, companies rebrand, and acquisitions fold one domain into another. When a domain stops publishing mail (MX) records, every address on it fails at once. When a domain lapses and someone else registers it, the new owner may receive mail meant for the old one, or may set it up specifically to catch it.

Typos and fake signups were never valid

Some “decay” was there from day one: mistyped addresses like jane@gmial.com, junk entries like test@test.com, and disposable inboxes that expire within hours. These don’t decay so much as get discovered the first time you mail them. M3AAWG’s Sender Best Common Practices warns that single opt-in lets typos and forged addresses onto lists unchecked, which leads to complaints and bounces.

Interest fades

Engagement decay has its own causes: you changed what you send, you send more often than people expected, or the reason they joined (a discount, a webinar, a free trial) has passed. These subscribers rarely unsubscribe. They just stop opening, and a few eventually hit “report spam” because it’s easier than finding the unsubscribe link.

What about the “your list decays X% per year” statistic?

You’ll see specific annual decay percentages repeated across many marketing blogs. Before relying on one, look for the original study: who measured it, on what kind of lists, in what year, and how they defined “decayed.” Many of these figures trace back to vendor reports with little published methodology, and some are many years old.

Your decay rate depends on your audience (B2B vs consumer, industry, seniority), how you collected addresses, and how often you mail. The only number that reliably describes your list is the one you measure.

How to measure email list decay on your own list

You can calculate a useful decay rate from data your email platform already has.

Method 1: Cohort bounce rate

Group contacts by signup quarter and send to them as usual. For each cohort, calculate the share of addresses that hard bounced on their most recent send.

Set up a sheet with one row per contact: column A signup date, column B status after the last send (“delivered” or “hard bounce”).

Add a cohort label in column C:

=YEAR(A2) & "-Q" & ROUNDUP(MONTH(A2)/3, 0)

Then build a summary table with each cohort in column E and calculate its hard bounce rate in column F:

=COUNTIFS($C:$C, E2, $B:$B, "hard bounce") / COUNTIF($C:$C, E2)

You’ll usually see older cohorts bouncing more than newer ones. The slope of that line is your technical decay.

Method 2: Engagement survival

Engagement decay is easier to see as “survival”: what share of each signup cohort has clicked in the last 90 days?

With last-click date in column D:

=COUNTIFS($C:$C, E2, $D:$D, ">=" & (TODAY()-90)) / COUNTIF($C:$C, E2)

Plot that by cohort. If people who joined a year ago are far less active than people who joined last quarter, your engagement decay is steep, and your re-engagement and sunset process needs to run more often.

Use clicks rather than opens where possible. Apple’s Mail Privacy Protection downloads remote content in the background by default, so opens overstate activity for many readers.

Method 3: Re-verify a sample

Take a random sample of an old segment, say a few hundred addresses, and check them. The share that fails domain or MX checks gives you a floor for technical decay on that segment. You can paste the sample into our free email verifier, which checks syntax, domain and MX records, disposable domains, role accounts, and common typos. It doesn’t connect to the mailbox itself, so it catches dead domains and broken addresses but won’t detect a single deleted mailbox on a working domain. Bounces from a real send will show you those.

How email list decay hurts deliverability

Decay isn’t just wasted sends. It shows up in the metrics providers enforce:

Decay type	What you see	Why it matters
Dead addresses	Hard bounces	Providers read high bounce rates as poor list management. Amazon SES reviews accounts at a 5% bounce rate.
Abandoned, repurposed addresses	Spam trap hits	Can lead to blocklistings and reputation damage
Uninterested subscribers	Low engagement, complaints	Gmail asks senders to keep spam rates below 0.10% and never reach 0.30%

M3AAWG’s glossary defines a “dirty mailing list” partly as one with poor handling of hard bounces or unsubscribes, or addresses that haven’t been mailed in a year or more. That last part is decay in action: a list left alone doesn’t stay as good as it was.

How to slow down email list decay

You can’t stop decay, but you can slow it and keep it from reaching your sending reputation.

Catch bad addresses at signup. Syntax checks, MX checks, and typo suggestions remove the “never valid” share before it’s saved.
Confirm new subscribers. Confirmed opt-in filters out typos and forged signups. See double opt-in vs single opt-in.
Mail consistently. Lists you contact regularly reveal dead addresses one bounce at a time. Lists you ignore for a year hand you all of them at once, in a single damaging send.
Suppress hard bounces automatically. Never retry a “user unknown.”
Ask B2B contacts to update their details. A preference center link like “Changing jobs? Update your email” saves some contacts who would otherwise be lost.
Run a sunset process. Re-engage, then retire, people who stop responding. See email sunset policy.
Verify before reactivating old segments. Anything that hasn’t been mailed in a long time should be checked before it goes back into rotation. How often should you verify your email list covers timing.

FAQ

How fast do email lists decay?

It depends on the audience. B2B lists lose addresses as people change jobs, and BLS data shows about a fifth of workers had been with their employer a year or less as of January 2026. Consumer lists lose addresses as people abandon inboxes. Measure your own rate by signup cohort rather than relying on a generic percentage.

Do B2B email lists decay faster than B2C lists?

Technical decay is often faster for B2B because work addresses are shut off when people leave. Consumer addresses tend to last longer but go quiet, so B2C lists frequently see more engagement decay than outright bounces.

Can an email address become valid again after it bounces?

Sometimes. A provider may let someone reclaim an address, or a new employee may get a reused name at a company. But a bounced address that later accepts mail could also be a recycled spam trap, so treat hard-bounced addresses as permanently suppressed.

Does verifying my list stop list decay?

No. Verification tells you which addresses look dead today. Decay continues the moment you finish, which is why ongoing bounce suppression and engagement-based sunsetting matter more than one-time cleanups.

Email List Decay: Why Email Lists Go Bad Over Time