The Dangers of Deleting Lists
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It’s possible to delete a list, but we don’t always recommend it. In this article, you’ll learn about the downsides of list deletion, along with some helpful alternatives.
Drawbacks of List Deletion
Permanent Data Loss
If you delete a list, you'll lose the list history—including subscriber activity, unsubscribes, complaints, and bounces. You’ll also lose subscribers’ email addresses, unless you exported a backup copy of your list. All campaigns that were sent to that list will remain in the account and most of the statistics in your campaign reports will continue to update. However, some list-specific links and system tags, like unsubscribe links, will stop working. Conversations will no longer be accessible after you delete a list.
Possible Abuse Complaints
For each list in your account, we keep track of bounced and unsubscribed addresses and prevent them from being re-imported to that same list. If you delete the list, its bounce and unsubscribe information is lost. Those bad addresses could be imported to another list in your account, which may lead to abuse complaints and possible account suspension.
If you need to delete anyway, learn how to permanently delete your list. Keep in mind that the general life of a campaign is 30-45 days, so it's best to leave your list in the account for at least that long before you delete it.
Alternative Options
Auto-Update Your List
Instead of deleting a list and importing the same subscribers to another list, perform an auto-update import to add new subscriber information to an existing list. This way, you maintain and update your existing list, and keep all your list-specific data, unsubscribes, and cleaned addresses intact.

Maintain a Single List
If you work for several clients, it makes sense to manage multiple lists. But if you manage a single business with different audiences, you can use groups and other tools to manage a single master list without duplicating or losing valuable data.