Every send is a vote on your reputation. Mailing addresses that never existed, never opted in, or have not engaged in a year is how good domains end up on blocklists. Most deliverability crises start as a dirty list, not as a clever template.
Remove these first
- Hard bounces and known invalid syntax. Do it before the next campaign, not in a quarterly cleanup.
- Role accounts (info@, sales@) unless you have a documented B2B reason and permission.
- Complaints and legal suppression, immediately. A preference center that takes a day to sync is a complaint factory.
- Unengaged subscribers past your cutoff, often 90 to 180 days depending on how often you mail.
Unknown-user rate is the hygiene metric mailbox providers notice fastest. Keep it tiny. If a campaign spikes it, the source of those names is the incident, not the subject line.
Confirm before you blast
Double opt-in is still the cheapest insurance for consumer lists. For imported B2B lists, require a paper trail: who captured the address, when, and for what. Purchased lists are not a gray area. They are how you inherit spam traps.
If sales hands you an export from a conference scanner, that is not consent to a weekly newsletter. Put those names in a one-time, clearly identified follow-up, then require a real opt-in for ongoing mail.
Sunset instead of sudden silence
A short win-back sequence with an obvious preference center is fair. If they still do not engage, stop. Continuing to mail them to “keep the list large” is how complaint rates climb while revenue per send falls. A smaller list that replies is cheaper to send and easier to place.
Hygiene is a pipeline, not a project
Validate at capture. Recheck on import. Suppress on bounce events in near real time. Review role accounts and traps after any list append. If your ESP makes it easy to upload a CSV and send tonight, add a hold that a human has to clear for lists older than 30 days.
When a blocklist listing names trap hits, freeze campaigns, audit the source of those recipients, and only resume on recently confirmed mail. Hygiene after a listing is slower and more public than hygiene before one.
Role accounts and traps in B2B
B2B senders love role addresses because they look like coverage. They also concentrate risk: one sales@ alias can be a trap, a ticket queue that marks you as spam, or five people who never wanted the mail. If you must mail them, use a one-to-one thread and a named person as soon as you have one.
Watch for clusters: many unknowns at one domain after a scrape, or a vendor file that bounces at 8%. That is not a Monday problem. That is a source problem.
What “clean” looks like in numbers
On a mature, opted-in list, unknown users should be a fraction of a percent. Complaints should stay comfortably under 0.1% of delivered mail. If you cannot see those rates per campaign, you are flying on vanity metrics. Hygiene without measurement is a slogan.
