You cannot delete an email list that was used in an email marketing or survey campaign or one that is part of an automatic subscription on an event, membership, donation or survey page.
To determine if the list in question has been used in an email marketing campaign or survey go to Workspace>Email Marketing>Campaigns. You can select Actions>Export to Excel File. A column called "Lists" will be included on the spreadsheet. You can do the same in Workspace>Surveys/Forms>Surveys/Forms List.
If the email list is included in an email marketing campaign or survey, you won't be able to delete it.
If you delete the campaign or survey, then you can delete the list. Keep in mind that if you delete a campaign or survey, you will lose all historical data related to it. If you do not want to delete the campaign or survey you can edit the list to make it inactive.
If you have set up an automatic assignment to an email list on one of your pages, this will also prevent you from deleting the email list. You can check the following on you pages to ensure the email list you wish to delete has not been used on one of your pages including any:
- Donation Page Settings Tab > Additional Options: Subscribe Donor to Email List
- Event Page Setup Tab > Ticket Level: Subscribe to Email List
- Membership Page Setup Tab > Membership Level > Advanced: Subscribe to Email List
- Survey/Form Page Settings Tab: Email List