How fast does an email list decay? The one recent, dated primary figure we could find comes from Hunter. In an eight-week experiment published on 4 November 2025, 5.5% of addresses that had passed verification degraded: 2.3% became invalid and 3.2% turned accept-all.
Eight weeks is a short window, and that's what makes the figure useful. A list verified in spring is measurably different by summer, before anyone has sent it a single campaign.
You'll also see an annual decay figure in almost every article on the subject, usually between 20% and 30% and usually with no primary source attached. We looked for one and couldn't trace it. A number nobody can trace isn't a measurement of your list.
Addresses don't expire on a schedule. They stop working for specific reasons, and those reasons run at different rates depending on who is on your list.
On a business list the largest cause is people changing jobs. The address belongs to the employer and goes when the person does, usually with no forwarding and no notice. That rate follows staff turnover in the sector rather than anything about email.
On consumer lists the causes differ. ISP mailboxes die with the broadband contract, which is why comcast.net and orange.fr addresses decay in a way gmail.com addresses don't. Free webmail accounts are rarely deleted, so they stay technically valid while nobody reads them.
Re-verification intervals by list type
B2B lists: before any large send if the data is more than eight weeks old. Staff turnover is the driver, and Hunter's 5.5% figure covers exactly that window.
Consumer lists: annually is usually enough, plus a check before any campaign that follows a long gap.
ISP-heavy consumer lists: more often, because the mailbox dies with the contract and nothing tells you.
Free webmail: validity holds up well and engagement doesn't. Verification keeps saying valid while the address sits unread, so your own open data is the better signal.
Any list: the share on catch-all domains drifts upward. When a company changes its mail routing to accept everything, a verdict of valid on its addresses quietly becomes catch-all, and the next check shows it.
Re-checks with ZapBounce cost only for answers: unknowns and duplicates are never billed, and credits never expire, so a pack bought for the spring check still covers autumn.
Why a single annual decay figure misleads
The short version
- Re-verify any B2B list older than eight weeks before a large send.
- Set frequency by list type: staff turnover drives business decay, closed ISP contracts drive consumer decay.
- Use engagement data for free webmail, where validity outlives usefulness by years.
Questions people ask
What is the average email list decay rate?
The one recent dated primary figure is Hunter's: 5.5% of verified addresses degraded in eight weeks, published 4 November 2025. Of that, 2.3% became invalid and 3.2% turned accept-all. The 20% to 30% a year quoted widely has no primary source we could trace.
How often should I re-verify an email list?
Before any large send to B2B data more than eight weeks old, annually for consumer lists, and whenever a list has sat idle. Frequency should follow the decay mechanism rather than a calendar rule.
Why do verified addresses turn catch-all?
Companies change their mail routing. A domain that rejected unknown recipients last quarter can switch to accepting everything, often during a move between mail platforms, and then every address on it returns 250. In Hunter's eight-week experiment, 3.2% of verified addresses turned accept-all.
Do valid addresses become invalid gradually?
No, they change state abruptly. Someone leaves a job, a contract ends, an account is closed. Decay looks gradual in aggregate and is a series of discrete events underneath.