Why two different users of similar emails were recognized as the same one?

We are using zendesk user api to create new users. Before we create a new user, we search if the user email already exists. If not, we create a new user. Otherwise, we update the existing user profile. 

Here comes the issue.

The email earcutcat133@gmail.com and the email earcutcat@gmail.com was recognized as the same user by zendesk api. 

How can we avoid this issue?

Is it possible to create two users with these two emails?