List Quality & Acquisition Integrity

Who you send to matters more than any other part of deliverability. This article explains how a poor list hurts you, which ways of collecting addresses are safe, and how to keep a list clean over time.

Why your list matters most

A perfectly authenticated email with great content still harms your reputation if it goes to people who don’t want it. A plain text email to people who asked for it will do better than a polished campaign sent to an old list.

The reason is that your list controls the signals providers weigh most heavily: how many emails bounce, how many people report you as spam, and how many people read your mail.

What a poor list does

Bounces

A bounce is an email that can’t be delivered. A hard bounce means the address doesn’t exist. A soft bounce is a temporary problem, such as a full mailbox.

Many hard bounces tell providers you don’t check your addresses, which is typical of spammers. Most ESPs start to worry when hard bounces go above 2% of a campaign. A clean list stays well below that. Go too high and providers may start rejecting all your mail, not just the bad addresses.

Spam complaints

A complaint happens when someone clicks “Report spam” or “Junk”. It’s the most damaging signal you can get.

• Aim for under 0.1%, or 1 complaint per 1,000 emails. This is Google’s recommendation.
• Never reach 0.3%. Gmail and Yahoo require bulk senders to stay below it.

People report mail as spam when:

• They don’t remember signing up.
• They never signed up (the address was bought, scraped or guessed).
• The emails aren’t what they expected.
• They can’t find the unsubscribe link.
• You email them too often.

Engagement

Engagement means what people do with your mail: open it, click it, reply, or ignore it. Providers watch both the good and the bad. If much of your list never reads your mail, providers learn that your mail isn’t wanted. Your next campaign then starts with a lower score, even for the people who do read it. See Engagement Economics for more.

Spam traps

A spam trap is an email address that exists only to catch senders with bad list habits. There are three kinds:

• Pristine traps never belonged to a real person. You can only get one by buying, scraping or guessing addresses. Hitting one is very damaging.
• Recycled traps were real addresses that were abandoned. After a long quiet period, the provider turned them into traps. Hitting one shows your list has old addresses you haven’t checked.
• Typo traps are misspelled domains, such as jane@gmial.com. They catch senders who don’t check addresses when people sign up.

Trap lists are secret, so you can’t look them up. The only protection is collecting addresses properly and cleaning your list regularly.

Where addresses come from

How you collect addresses sets the quality of your list from the start. Here are the common methods, from best to worst.

Double opt-in (best)

The person enters their address, then clicks a link in a confirmation email. Only then are they added. This is also called confirmed opt-in.

It proves two things: the address works, and the owner wants your mail. Typos, bots and sign-ups made by someone else never reach your list. Your list will grow more slowly, because some people won’t click. But it will bounce less and get far fewer complaints.

Single opt-in

The person enters their address and is added straight away, with no confirmation.

The risks:

• Typos stay on the list (john@gmial.com).
• Bots can fill your list with junk.
• Someone can sign up an address that isn’t theirs.

If you use single opt-in, check each address as it’s entered. A validation service can catch invalid addresses and obvious typos before they reach your list.

Implied consent

The person has some relationship with you (a customer, a free-trial user, an event guest), but never asked for your emails. You add them anyway.

Many people don’t expect marketing just because they bought something, so complaints run high. It can also be illegal. Laws such as GDPR in the EU and CASL in Canada set rules for when you may send marketing email, and the rules differ by country. See Legal. Messages about the relationship itself, such as order updates and account notices, are fine.

Bought or rented lists (never)

Lists bought from a third party:

• Are full of invalid addresses, so bounces spike.
• Often contain spam traps.
• Get many complaints, because the people have never heard of you.
• Break the rules of almost every ESP.
• Usually break consent laws such as GDPR and CASL.
• Can get you blocklisted quickly.

Don’t buy lists.

Scraped addresses (never)

Copying addresses from websites, forums or directories without asking is spam. It breaks anti-spam laws and every ESP’s rules, and it will wreck your reputation.

Keeping your list clean

Every list decays. People change jobs, abandon accounts and lose interest. Cleaning is ongoing work.

Remove hard bounces at once

An address that hard bounces doesn’t exist. Remove it after the first hard bounce. Most ESPs do this for you, but check that their suppression list (the list of addresses they won’t send to) is working.

Watch soft bounces

Soft bounces are temporary, so your ESP retries for a day or so. If the same address soft bounces in three or more campaigns in a row, stop sending to it. A mailbox that is always full is often abandoned.

Stop emailing people who never engage

This is the most important habit. Group people by when they last opened or clicked:

• Active: in the last 90 days.
• At risk: 90 to 180 days ago.
• Dormant: more than 180 days ago.

Then:

1. Send people at risk a win-back email: “Do you still want our emails?”
2. Move anyone who doesn’t respond within 30 days to a dormant group.
3. Send dormant people one last attempt, then stop emailing them.
4. Remove anyone with no activity for a year.

It feels odd to shrink your own list. But emailing people who ignore you hurts your delivery to the people who read you. A smaller, active list reaches the inbox more often.

Check your list now and then

Run your list through a validation service from time to time. It can:

• Find addresses that have stopped working.
• Flag role addresses like info@ or admin@, which are shared by several people and complain more.
• Remove throwaway (disposable) addresses.

Act on complaints

A feedback loop (FBL) is a service where a provider tells you each time one of its users reports your mail as spam. Sign up where you can:

• Yahoo: the Complaint Feedback Loop covers Yahoo and AOL users.
• Microsoft: JMRP (Junk Mail Reporting Program) covers Outlook.com and Hotmail users.
• Gmail doesn’t report individual addresses. You see your overall spam rate in Google Postmaster Tools.

When someone complains, stop emailing them right away. Mailing them again only brings more complaints.

Send the right mail to the right people

Segmenting means splitting your list into groups and sending each group what fits. Relevant mail gets fewer complaints and more reads, which improves your reputation.

Common ways to split a list:

• By engagement: send your most active readers more often. Send quiet readers less, and only your best content.
• By stage: new subscribers get a welcome series. Customers get product news. Lapsed customers get a win-back offer.
• By choice: let people pick how often they hear from you and which topics they get.

Measuring list quality

Check these after every campaign, and watch how they change over time:

Measure	Healthy	Worrying	Serious
Hard bounces	under 0.5%	0.5–2%	over 2%
Spam complaints	under 0.1%	0.1–0.3%	over 0.3%
Open rate	over 20%	10–20%	under 10%
Click rate	over 2%	1–2%	under 1%
Unsubscribes	under 0.3%	0.3–0.5%	over 0.5%

The complaint limits come from Gmail and Yahoo. The others are rough guides, so compare them with your own past results. Open rates are unreliable: Apple Mail Privacy Protection loads the images in emails in advance for people who turn it on, so many emails count as “opened” even if nobody read them. Leave Apple Mail users out when you judge open rates.

A healthy list gains new subscribers faster than it loses old ones. If yours keeps shrinking from bounces and unsubscribes, look at how you collect addresses and what you send.

Checklist

• Use double opt-in, or at least check addresses as they’re entered.
• Never buy, rent or scrape addresses.
• Remove hard bounces after the first one.
• Stop sending to addresses that soft bounce again and again.
• Run win-back emails, then stop emailing people who don’t respond.
• Sign up for feedback loops, and stop emailing anyone who complains.
• Segment by engagement, stage and preference.
• Track bounces, complaints and engagement for every campaign.