How do I import users and delete their emails?

[Opserty]

You'll probably need a PHP script or something to update the emails to something unique.

If you just want to change all the emails to the same thing you can run a query after you have imported the database.
[sql]
UPDATE `user` SET `email` = 'SOMESTRING@SOMESTRING.COM'
[/sql]

Although if you want to get a little more complex you could use PHP to generate a random like email address.