Cleaning your list before the first send through a new platform

Before the first send through a new platform you remove five things from your list: addresses that hard-bounced on the old platform, unsubscribers and complainers, addresses without any activity in the past year, invalid and role-based addresses (such as info@ or noreply@), and duplicates. What remains you split by engagement, so that the first sends only go to your best recipients. The reason: your new sending environment has no history with the providers yet, and the first weeks determine how they treat you for the coming months.

Why right now

On your old platform you carried an established reputation that absorbed small mistakes. On the new platform your domain starts with a new DKIM signature from different IP addresses; the receiving providers see a new combination and watch more closely. An old list with dead addresses and spam traps that "still worked" on the old platform is, in those first weeks, a risk that can cost you months.

Step 1: bring the suppression list along

The most important thing to export from the old platform is not the list itself but the list of who you may no longer mail: hard bounces, unsubscribers and people who reported spam. Almost every platform can export those separately. Import them on the new platform as a suppression list before you import a single address from the regular list. That way an unsubscriber can never accidentally come back onto the list through a later import from your CRM.

Step 2: remove what no longer exists

Hard bounces from the last twelve months are in the suppression list from step 1. Also look at:

• Syntactically invalid addresses. Missing @, spaces, commas instead of dots. A simple check in a spreadsheet catches them.
• Domains without a mail server. A domain without an MX record cannot receive mail. A sending platform or a small script can check that per domain; on a list with many old business addresses that yields surprisingly much.

Step 3: role-based and suspicious addresses

Addresses such as info@, admin@, sales@, noreply@ or postmaster@ are not people. They are read by several people or by nobody, and they often sit on lists without anyone ever having given consent. Take them out of your campaign list; for transactional mail (an invoice to accounts@) they are of course still valid.

Step 4: activity and consent

This is the step that yields the most and meets the most resistance. Addresses that opened or clicked nothing in the past year and bought nothing you do not mail on the new platform, at least not in the first weeks. They lower your engagement figures with the providers and contain part of the spam traps that old lists accumulate: addresses that were once real and were reused as a trap by a provider after years of inactivity. What a spam trap exactly is you can read in our article on that; here it suffices that you cannot recognise them by the address itself, only by the pattern of years of silence.

Check consent at the same time. For every address you must be able to say when and where it signed up. Addresses without origin, from an old trade fair export or a bought list, should not move with you.

Step 5: deduplicate and normalise

Put all addresses in lower case and strip leading and trailing spaces; otherwise your platform sees Jan@example.be and jan@example.be as two recipients and Jan gets everything twice. Remove duplicates across all your sources (webshop, CRM, old newsletter tool) and keep per address the earliest sign-up date and origin.

Afterwards: split and build up

What remains you divide into three groups: active in the past three months, active in the past six months, active in the past year. The first sends go only to group one; the other groups are added in the following weeks as long as the figures stay good. That is essentially a warm-up of your domain, and it is the reason you do not only clean the list but label it as well. How to set that up in the campaign tool is on our page about list segmentation.

Also get the technical side ready before the first send: SPF, DKIM and DMARC for the new platform, an unsubscribe link that works, and test addresses at the large providers. On an SMTP relay with bounce processing and logging you see per domain what happens from the very first send, and you can adjust the build-up accordingly.

An example

A wholesaler moves a list of 42,000 addresses. After the suppression list (3,100 bounces and unsubscribers) and the technical check (900 invalid addresses and domains without a mail server), 38,000 remain. Of those, 21,000 had no activity of any kind in the past year. The first send goes to the 6,500 addresses that clicked or ordered in the past three months. Three weeks later the wholesaler mails the full active group of 17,000, with a bounce rate that is a fraction of what the old platform showed. The 21,000 inactive addresses later get one reactivation mail; whoever does not respond is archived.

Frequently asked questions

Should I use a paid address verification service?

Those services check whether a mailbox exists without sending mail to it. They are useful for a large, old list, but do not replace step 4: an existing address that has not read for years remains a bad address.

What if my old platform cannot export a suppression list?

Then export at least the unsubscribers and bounces from the reports of the last campaigns. Our page on comparing email platforms lists what to watch for when switching.