Hibernate ManyToOne JOIN by non-PK column throws "Bad value for type int"

First of all let me make my scenario clear I am using hibernate 4.3 ,Postgresql 9.3 with spring MVC ,and I have reverse engineered classes using JBOSS tool.

Every time I select the data using HQL or session.get() I am getting (SQL queries are working fine) Caused by : org.postgresql.util.PSQLException: Bad value for type int : demoemailaddr@gmail.com

my first entity classes,

Applicant.java

@Entity
@Table(name = "applicant", schema = "public", uniqueConstraints = { @UniqueConstraint(columnNames = "user_id"), @UniqueConstraint(columnNames = "email"), @UniqueConstraint(columnNames = "registration_id") })
public class Applicant implements java.io.Serializable
{
    @Id
    @Column(name = "application_id", unique = true, nullable = false, length = 7)
    private String applicationId;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "email", unique = true, nullable = false)
    private Users usersByEmail;

     // setters and getters
}

and Users class which has @ManytOne relationship with above class.

@Entity
@Table(name = "users", schema = "public", uniqueConstraints = { @UniqueConstraint(columnNames = "email"), @UniqueConstraint(columnNames = "application_id") })
public class Users implements java.io.Serializable
{
    @Id
    @Column(name = "user_id", unique = true, nullable = false)
    private int userId;

    @Column(name = "email", unique = true, nullable = false, length = 100)
    private String email;

}

Now check the schema structure

CREATE TABLE users
(
  email character varying(100) NOT NULL,
  user_id integer NOT NULL,
  CONSTRAINT users_pk PRIMARY KEY (user_id),
  CONSTRAINT unique_email UNIQUE (email)
)

 CREATE TABLE applicant
(
  application_id character(7) NOT NULL,
  email character varying(100) NOT NULL,
  CONSTRAINT users_email_fk FOREIGN KEY (email)
  REFERENCES users (email) MATCH SIMPLE
  ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT unique_applicant_email UNIQUE (email)
 )

[Edited] I am using join column on email of user table which has Unique constraint but not it's not PK(PK is user_id)

PS:I can't change db schema structure, I don't have authority