Petros

When Petros was thirty, he was hired by a sender who had bought a list of 100,000 contacts. They wanted him to validate it and clean it. They had paid a lot for the list. They had a campaign launching in two days.

He ran his checks. The list had a 31% bounce rate. Twelve known spamtraps. Two of them were the Spamhaus pristine traps, addresses no real person has ever owned. Sending to even one of those would put the sender on Spamhaus within a week.

He told them to scrap the list. They told him he didn't understand the urgency. He told them he understood very well, and walked away from the contract. He didn't raise his voice. He just left the coffee on the table and walked out.

The sender ignored his advice. Sent the campaign. Got blocklisted by the end of the month. The company pivoted to a new domain three months later.

Petros lost the contract. He also kept his reputation. A list you should not send to is not a list. It's a trap dressed as a list.

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A small ecommerce shop hired Petros in a panic. Their open rates had dropped from 24% to 6% in six weeks. Revenue was down 40%. They thought their content was the problem. They had hired a copywriter and were ready to pay for a "complete brand refresh."

He asked them when they'd last cleaned. The answer was "we don't really do that."

He validated the list. 23% of it was dead. Four spamtraps. Eighteen percent had been inactive for over two years. After the clean: list size went from 138,000 to 91,000.

The next campaign hit a 28% open rate. Higher than they'd ever had.

He didn't get a bigger fee for the bigger result. He got a thank-you card and a tin of pasteli. That was enough. The list was clean. The garden grew the right thing.

Petros's intro:

I get asked this more than anything. "What is list hygiene?" Usually it's a polite way of saying "I don't really do this and I don't want to feel stupid asking." So I'll say it plain. There's nothing to feel stupid about. Most senders don't do this. That's why most senders have problems.

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A list is a record of people who said you could email them. List hygiene is the work of keeping that record honest.

Every email list rots. It rots because people change jobs and abandon their work addresses. It rots because companies fold. It rots because some addresses were never real to begin with, just typos at signup. It rots because some addresses were real, then went quiet, then got reactivated by an ISP as a spamtrap to catch lazy senders.

Hygiene is the practice of removing the rot before it spreads.

There are three pieces to it.

Validation. Finding out which addresses on your list are broken. There are tools for this. They check whether the address still accepts mail, whether the domain still exists, whether the format is even legal. A good validation pass on a list that hasn't been cleaned in a year typically finds 8-25% of the addresses are dead.

Removal. Once you know which addresses are dead, you take them off the active list. You don't delete them outright. You move them to a suppression list. That's a separate hold where you keep the addresses you've promised never to email again. Suppression lists matter because dead addresses sometimes come back. People return to old jobs. Companies un-fold. You want to know whether you've already burned a bridge.

Engagement-based pruning. This is the harder one. Not all problem addresses are dead. Some are alive but bored. They haven't opened or clicked an email from you in two years. They didn't unsubscribe, they just stopped paying attention. To you they look the same as engaged subscribers in your dashboard, but to ISPs they look like a sign of an unhealthy list. You should move them out of the main list, attempt to win them back, then suppress the ones that don't respond.

That's hygiene. Validation, removal, pruning.

Why do it? Three reasons.

First, ISPs use list health to decide whether your emails reach the inbox or the spam folder. A list with 5% bounces and 60% disengaged subscribers tells Gmail something specific about you. None of it is good.

Second, you pay for every address on most ESP plans. A list that's 22% dead is 22% of your bill being charged to nothing.

Third, sending to addresses that have been turned into spamtraps will land you on a public blocklist within a week. Once you're listed, your domain is functionally dead for marketing email until you get delisted, which takes 30-90 days minimum, and your reputation never fully recovers.

So hygiene is performance, cost, and risk all in one. Senders who do it look healthy. Senders who don't, don't.

How often? Once a quarter is the floor for most senders. Once a month for high-volume or B2B senders. After any major data import, immediately. Before any major campaign, immediately. The rule is "before sending into anything important, clean."

That's the whole thing. Validate, remove, prune. Quarterly, manually or with automation. Easier than it sounds. Most senders don't do it.

You're already ahead by reading this.

- Petros

Petros's intro:

This one is for whoever just got handed a list and a job and was told "make it work." I get it. I've cleaned 47 lists I didn't build. Here's what I do, in order.

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You inherited a list. Maybe you took over a marketing role. Maybe you bought a company. Maybe a colleague left and the list is now your problem. You don't know who built it, you don't know how clean it is, and you have a campaign to send.

Don't send the campaign. Not yet. Six steps first.

Step 1. Find out how big the list actually is

Pull the full list out of whatever ESP holds it. Get a count. Not the "active subscribers" count the dashboard shows, the actual record count. Sometimes those numbers don't match. The dashboard might exclude unsubscribes or suppressed addresses. You want all of them, including the ones already flagged as do-not-send. Knowing where you are starts here.

Step 2. Pull the engagement history

Find out, for each address, how recently they opened or clicked. If your ESP doesn't expose this, find one that does. Many will export a report with "last open date" and "last click date." Get those columns. Anyone who hasn't engaged in 12+ months is a suspect. Anyone who hasn't engaged in 24+ months is a problem.

Step 3. Run a validation pass

Use a real validation service. The cheap ones miss things. The expensive ones don't. For a 10,000-address list, expect to pay $30-100. The validator will tell you which addresses are: confirmed valid, confirmed invalid (hard bounces in waiting), risky (catch-all domains, role accounts, addresses that look like typos), and unknown (couldn't verify, treat with caution).

For an inherited list, expect 8-30% of the list to come back invalid or risky. The age of the list determines where you fall in that range.

Step 4. Make three buckets

Take the validation output and split the list into three:

- Keep: confirmed valid AND engaged within the last 12 months - Watch: confirmed valid but disengaged 12-24 months - Suppress: invalid, risky, OR disengaged 24+ months

The Keep list is what you'll send to. The Watch list is your re-engagement target. The Suppress list goes into your suppression file forever.

Step 5. Run a re-engagement campaign on the Watch list (NOT the Keep list)

Send the Watch list a single re-engagement email. One. Not a series. Not a "we miss you, here's a discount." A clear note that says "we noticed you haven't opened our emails in a while. If you'd still like to hear from us, click here. If we don't hear back, we'll stop sending."

Then mean it. The ones who click move into Keep. The ones who don't move into Suppress. Give them 14 days to respond.

Step 6. NOW you can send the campaign

To the Keep list only. Not the Watch list, not the Suppress list. The Watch list is in re-engagement mode. The Suppress list never gets contacted again unless they actively opt back in through a website form.

This whole process takes about 3-4 weeks. You will lose a significant chunk of your list, possibly 25-50%. Your remaining list will perform better than your original list ever did. Higher open rates, higher click rates, lower complaints, lower spam folder placement.

The first time you do this it will feel painful. It is not painful. It is the only honest way to inherit a list. The alternative, which I've seen many times, is sending to the inherited list as-is and burning the domain reputation in a single campaign. Most senders who skip this end up needing to migrate to a new domain within six months.

Better to lose 40% of the list and keep the domain.

- Petros

Petros's intro:

This one is short because the math is short. But the math is the whole point. People don't know how fast lists die.

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Here's a number to sit with: B2B email lists lose roughly 22.5% of their addresses every year just from people changing jobs.

That's the average employee turnover rate across knowledge industries. Sales people leave companies. Marketers move agencies. Engineers go to startups. Every time someone leaves a company, their work email becomes either a dead address or a role address that someone else inherits. Either way, the original consent is gone.

22.5% per year compounds. Run the math:

- After 1 year: 77.5% of the list is still valid - After 2 years: 60% of the list is still valid - After 3 years: 47% of the list is still valid - After 4 years: 36% of the list is still valid

If you've been holding a B2B list for four years and haven't cleaned it, more than half of the addresses on it are no longer who you think they are. Some are dead. Some belong to different people now. Some have become role addresses that fifteen people read indifferently. None of them are the people who originally subscribed.

For B2C lists the rate is lower. People change personal email addresses about 7-10% per year. So a B2C list ages slower, but it still ages.

Why this matters: senders look at their list size and feel rich. "I have 50,000 subscribers." A list of 50,000 that hasn't been cleaned in three years is functionally a list of about 23,000 real people, plus 27,000 records that are dead, mismatched, or worse. Sending to the 27,000 is what triggers blocklists, what kills your domain reputation, what costs you the 23,000 too.

The fix is not glamorous. Once a quarter, run a validation pass. Once a year, re-engagement campaign. Once every two years, a hard suppression sweep on anyone who's gone fully dark.

Senders who do this maintain a list that performs above industry benchmarks indefinitely. Senders who don't, lose the list slowly, then suddenly.

The math doesn't care how nice your campaigns are. The math is the math.

- Petros