Membership on a list can be modified in bulk. Start by Logging In to the online interface, then click Review Members
Delete in Bulk
Finally, click Delete selected email addresses
This will remove all the members from the list on that page. If your list has more members, the screen will reload and show the next set of members.
To speed up the process, set the page size to 500
Repeat until you get a message that the list has no members.
Add in Bulk
To add many users at once, click the Multiple Add button in the add user section
You’ll be taken to a screen with a yellow box for pasting multiple entries. The example in the box will go away when you click in that box.
When pasting, the information should be in this format:
email@example.com FirstName1 LastName1
firstname.lastname@example.org FirstName2 LastName2
The names are optional. You are limited to 1,000 entries at one time, but this can be repeated as needed.
With entries in the yellow box, click “quiet”
The list will report back the number of subscribers.