Keep Your Subscriber List Healthy

A list starts decaying the day you import it. Mailboxes close, domains lapse and people stop reading. A little upkeep keeps your sends out of the spam folder, and keeps your tests honest: every bounced or ignored email is one fewer that can show a difference.

This is part 3 of a three-part series. Part 1 built the list and part 2 explained who in it you may email. This part covers the upkeep, most of which MailInApp does for you.

The examples follow Retro Revival, a fictional vintage clothing shop, with made-up numbers.

What happens on its own

Some upkeep needs nothing from you:

• Hard bounces. When a message bounces because the mailbox doesn't exist, the address is suppressed for your whole account and marked invalid on every list that holds it. If you send through your own SMTP server, only a refusal saying the mailbox doesn't exist counts. A wrong password or a server that's down doesn't suppress anyone.
• Spam reports. Someone who marks your email as spam is suppressed as if they had unsubscribed.
• Unsubscribes. The footer link suppresses the address across every email you send.
• New addresses. Every address that enters a list, by import, signup form, API or store sync, is checked as it's saved.

Re-check a list

Domains stop accepting mail over time, so an address that was valid at import can go bad. Open the list under Contacts. The Email verification panel above the grid shows a quality bar for the whole list.

1. Click Verify list. A large list is checked in the background.
2. Review what was found with the filter chips: all, valid, risky, invalid.
3. Click Remove with the number of invalid addresses to delete them. This can't be undone.

The free check looks at each address's format and domain. If you have a ZeroBounce or NeverBounce account, connect it under Settings → Integrations → Data providers to also check individual mailboxes, using your own credits.

The list-quality gate

If more than 5% of a send's recipients are invalid or couldn't be checked, a manual send stops with This list needs cleaning before you send. Click Verify this list, or tick the acknowledgement and Send anyway. Sending anyway is recorded in your account's audit log, and invalid addresses are still skipped.

Recurring sends and journeys don't stop, since nobody is there to answer. They skip invalid addresses and send you a push alert, at most once per list per day.

Retire the people who stopped reading

Mailbox providers watch whether people open and click your mail. Sending again and again to people who ignore it tells them your mail isn't wanted, which hurts delivery for the whole list.

The sunset policy handles this. Under Sunset policy in Settings, it finds contacts with no opens, clicks or orders for 60 to 180 days (90 by default). It can enrol them in a re-engagement journey first, such as a last-chance scratch-off, and then suppress those who still don't respond. Start with the journey alone for a month. Check how many came back, and only then turn on automatic suppression.

Keep the attributes current

Columns go stale too. A prospect who buys becomes a customer, and tastes change. Keep the columns you target and balance on up to date:

• Update customer_type from your store or CRM through the contacts API, which changes only the fields you send. A re-import doesn't update contacts that are already in the list.
• Let subscribers update their own interests through a poll or form that saves its answer to a contact field.

Why this matters for a test

An experiment compares arms on the emails that were delivered, and plans its sample with your expected delivery rate. The planner reads that rate from your sends of the last 90 days. A list full of dead addresses needs more contacts for the same test, and loses more of them on the way.

Retro Revival cleaned its list before its reward test. 40 emails per arm of 2,000 still bounced, so 1,960 per arm were delivered: a 98% delivery rate, which the planner had assumed. Each arm also lost the same share, which the results page's data-quality checks confirm.

A monthly routine

1. Open each list you send to and click Verify list. Remove the invalid addresses.
2. Look at the Left out breakdown of your next send or experiment. A growing "Unsubscribed or bounced" share deserves a look at what you're sending.
3. Check the sunset policy's journey: how many came back, and how many were suppressed.
4. Sync customer_type and any other balance fields from your store or CRM.

Getting started

Open your largest list under Contacts and run Verify list today. Then turn on the sunset policy with a re-engagement journey, and put the monthly routine in your calendar. With a clean list, your next experiment's delivered count is close to its sample, and its results describe people who actually read your email.