Validate email address properly

app/models/user.rb

@@ -1,10 +1,13 @@
 class User < ApplicationRecord
+  include EmailValidatable
+
   # Relations
   has_many :invitations, dependent: :destroy
 
   validates_uniqueness_of :cn
-  validates_uniqueness_of :email
   validates_length_of :cn, :minimum => 3
+  validates_uniqueness_of :email
+  validates :email, email: true
 
   # Include default devise modules. Others available are:
   # :confirmable, :lockable, :timeoutable, :trackable and :omniauthable