Email list decay: how fast do email lists go bad and what to do

Email list decay is the steady loss of valid, reachable addresses from a list over time, and a typical list loses around 22% to 30% of its deliverable addresses every year. B2B lists decay faster than B2C because work addresses die when people change jobs, while consumer mailboxes last for years. Left unchecked, a 10,000-contact list has roughly 7,800 working addresses after a year and about 6,000 after two, and every one of the dead addresses is a hard bounce waiting for your next campaign.

How fast does an email list decay?

The commonly quoted figure is around 22% a year, and that is a reasonable planning number for a mixed list. B2B lists built from work addresses sit at the high end, often 25% to 30% a year, with some sectors (recruitment, agencies, startups) losing a third. Consumer lists built on Gmail, Outlook.com and Yahoo addresses decay more slowly, perhaps 10% to 15% a year, because people keep personal mailboxes for a long time even if they stop reading them.

Decay is also not linear. A list collected at a conference loses addresses fastest in the first year, because the people who were about to move on do so, and then settles. A list that has not been mailed at all decays invisibly: nothing bounces because nothing was sent, and the dead addresses pile up until the day you import it somewhere new.

Why do addresses go bad?

• Job changes. The dominant cause on B2B lists. The mailbox is deleted, and from that point every message hard bounces with 550 5.1.1.
• Abandoned mailboxes. People open a mailbox for one purpose and walk away. It may be closed by the provider after a period of inactivity, or left open and full, soft bouncing forever.
• Company changes. Mergers, rebrands and closures change or retire whole domains. Every address at the old domain dies at once.
• Domain changes. A small business moves from a free provider to its own domain, or lets a domain lapse.
• Provider cleanups. Free providers close long-inactive accounts; some of those addresses later return as spam traps, which is covered in what is a spam trap.
• Bad data at capture. Typos and fake addresses are dead on day one but count as decay when they are discovered later.

What does decay do to a 10,000-contact list?

Assume a list of 10,000 valid addresses on the day it is verified, and compound the loss monthly.

Now look at what that means for a send. Mail the full list after 12 months without cleaning and you send 10,000 messages of which 2,200 to 3,000 hard bounce: a bounce rate of 22% to 30%, more than ten times the 2% level at which mailbox providers start throttling. Even after six months the raw bounce rate would be 12% to 16%. In practice ESPs remove bounces as they happen, so a regularly mailed list never shows those figures, but a list that has sat idle for six months or more will.

The rows also show why "we cleaned it last year" is not enough. A list verified 12 months ago has already replaced a fifth to a third of its valid addresses with dead ones.

How do you measure your own decay rate?

You do not need to guess. Two methods, one quick and one accurate:

1. Bounce method. Take the hard bounces from the last three months of campaigns, divide by the number of unique addresses mailed, and multiply by four. If 50,000 addresses produced 2,750 hard bounces in a quarter, that is 5.5% a quarter, or roughly 22% a year. This undercounts slightly because ESPs suppress addresses after the first bounce.
2. Verification method. Take a segment that was verified at a known date, re-verify it now, and count the addresses that moved from deliverable to undeliverable. Divide by the months elapsed. This is the accurate figure, and it also tells you which segments decay fastest. A 2,000-address sample is enough; the bulk email verifier will run it in a few minutes.

Segment the result by source and by domain type. Free-provider addresses, corporate addresses and addresses from each capture channel decay at different rates, and the fastest-decaying segment is the one to re-verify most often.

How often should you re-verify?

A cadence that matches the decay rate keeps the bounce rate under 0.5% without verifying addresses that do not need it.

• Active lists mailed at least monthly: re-verify every 90 days. At 22% a year, 90 days of decay is about 6%, which is enough to push an unmaintained segment past the 2% line if the bounces cluster.
• Any list or segment not mailed in six months: verify before every send until it is active again. The idle period is where decay goes unnoticed.
• Imported, exported or migrated lists: verify on import, regardless of age. A list moving between ESPs loses its bounce history on the way.
• Signups: verify at the form with real-time checks, so new addresses start at zero decay rather than carrying typos in from day one.
• Cold outreach lists: verify within 30 days of use, because these are the fastest-decaying lists and the senders with the least reputation to spare.

Repeat checks of the same address within 24 hours are free on Verifyre, so re-running a segment you verified yesterday costs nothing; the credits go on addresses that have had time to change. The full maintenance routine is in the email list hygiene checklist.

What is a sunset policy and why does it matter?

Verification tells you whether a mailbox exists, not whether anyone reads it, and an abandoned-but-open mailbox is where decay turns into reputation damage: no bounce, no opens, and eventually a recycled spam trap. A sunset policy handles that half of the problem.

1. Define inactivity. No opens or clicks in 180 days for high-volume senders, 365 days for low-volume ones. Treat opens with caution since privacy proxies inflate them; clicks are the reliable signal.
2. Send one re-engagement series of two or three messages over two weeks, asking the subscriber to click to stay.
3. Suppress everyone who does not respond. Keep the record so they are not re-imported later, but stop mailing.
4. Verify the suppressed segment once a year before any attempt to win it back, so you never mail a recycled address.

Senders who combine a 90-day verification cycle with a 12-month sunset policy typically hold hard bounces at 0.1% to 0.3%.

Key takeaways

• Lists typically lose 22% to 30% of their valid addresses a year; B2B faster, B2C slower.
• A 10,000-contact list has about 7,800 valid addresses after 12 months and about 6,000 after 24 if nothing is done.
• Measure your own rate from quarterly hard bounces or by re-verifying a dated sample.
• Re-verify active lists every 90 days and any list idle for six months before every send.
• Pair verification with a sunset policy, because an open but unread mailbox is the other half of decay.

Frequently asked questions

Why does my list decay faster than 22%?

Usually because it is B2B, because it was built from a single event or campaign, or because the addresses were captured without validation. Startup, recruitment and agency lists commonly lose 30% or more a year.

Does decay stop if I mail the list regularly?

No, but it becomes visible. Regular sends surface bounces as they happen and the ESP suppresses them, so the active list stays clean while the suppressed segment grows. The underlying rate is the same.

Can I just rely on the ESP to remove bounces?

For hard bounces on addresses you mail, yes. For addresses you have not mailed in months, for full mailboxes that soft bounce indefinitely, and for lists you import or migrate, no. Those need bulk list cleaning before the send.