Overwriting existing users

Hi, this looks like the plugin I need, but I have a question:

I am importing a large number of users from a CSV, but some of them may have already registered. What will happen if I import a user with the same e-mail (or other info) as an existing user? Will the plugin overwrite that user, reject the new info, or fail to import?

Thanks.

site http://:egsa.ucdavis.edu

http://ww.wp.xz.cn/plugins/add-multiple-users/