B2B contact data decays at roughly 30% per year. Some industries are worse. Tech and SaaS churn faster. Professional services slightly slower. But across the board, nearly a third of the data you paid for twelve months ago is now wrong.
People change jobs. Companies restructure. Email addresses bounce. Phone numbers get reassigned. And that expensive list you bought from a data broker? It started degrading the moment they pressed export.
Most businesses treat data as a one-time purchase. Buy the list, load it into the CRM, run campaigns against it for the next two years. The maths on this approach is brutal.
Say you bought 5,000 contacts at 12p each. That's £600. Feels like good value. Now fast-forward twelve months. Roughly 1,500 of those contacts have changed roles, left their companies, or retired. Their email addresses bounce. Their phone numbers ring out. You're now marketing to 3,500 people, but you're still paying platform costs, sending costs, and staff time as if you had 5,000.
Worse, those 1,500 dead contacts aren't just useless. They're actively harmful. High bounce rates damage your sender reputation. Email providers notice when 20% or 30% of your sends bounce, and they start routing your emails to spam. Not just to the dead addresses. To everyone.
We ran verification on a year-old list for a client last quarter. Out of 4,200 contacts, 1,764 came back as invalid. That's 42%. Nearly half the list was dead weight, silently dragging down every campaign sent to it.
Data brokers sell volume. Their pitch is built around big numbers: "Access 50 million B2B contacts." What they don't emphasise is the shelf life. Most broker data is aggregated from multiple sources, some of which are themselves months or years old by the time they reach the final database. You're buying data that might already be stale before you receive it.
The better brokers will offer a "freshness guarantee" or claim regular verification. Some of these claims are genuine. Many are aspirational. Unless you're independently verifying the data yourself, you're trusting someone else's quality control with your sender reputation and campaign performance.
Proper data hygiene isn't glamorous. It's running every email address through a verification service before you send to it. It's checking phone numbers are still connected. It's cross-referencing company names against Companies House to confirm they're still trading.
This costs money and takes time. A full verification pass on a 5,000-contact list might cost £150 to £250, depending on the depth of checks. But compare that to the cost of a damaged sender domain that takes weeks to recover, or the opportunity cost of sales teams calling numbers that ring out.
The cadence matters too. Verifying once at purchase isn't enough. Quarterly verification for active campaign lists, annual verification for dormant lists. Anything less and you're guessing.
There's another option that most businesses don't consider: building your own data. Not buying a list from a broker, but systematically identifying and verifying prospects yourself.
It takes longer. It costs more upfront. But the data is yours, it's current, and it's tailored to exactly who you want to reach. You're not paying for 5,000 contacts in the hope that 500 are relevant. You're building 500 contacts that are all relevant.
I wrote about Companies House data mining in more detail later in the year. For now, the principle is simple: owning your data is almost always better than renting someone else's. Especially when someone else's is a year old and decaying.
If you have a contact list older than six months that you haven't verified, stop sending to it until you do. The cost of verification is a fraction of the cost of wrecked deliverability.
If you're buying data from a broker, ask when it was last verified, what their methodology is, and what the expected bounce rate will be. If they can't answer those questions clearly, find a different broker.
If you're not tracking bounce rates and complaint rates on your email campaigns, start. Those numbers tell you the health of your data more honestly than any broker's claims.
Data isn't an asset you buy once. It's a living thing that requires maintenance. Ignore it and it rots. Look after it and it compounds.
Martin Dugan, AA2
