Use base 64 encoding for email params.

app/controllers/unsubscribes_controller.rb

@@ -15,8 +15,9 @@ class UnsubscribesController < ApplicationController
   end
 
   protected
+
   def get_user
-    @email = CGI.unescape(params[:email])
+    @email = Base64.urlsafe_decode64(params[:email])
     User.where(email: @email).first
   end
 end

app/mailers/emails/admin_notification.rb

@@ -2,7 +2,7 @@ module Emails
   module AdminNotification
     def send_admin_notification(user_id, subject, body)
       email = recipient(user_id)
-      @unsubscribe_url = unsubscribe_url(email: CGI.escape(email))
+      @unsubscribe_url = unsubscribe_url(email: Base64.urlsafe_encode64(email))
       @body = body
       mail to: email, subject: subject
     end

app/views/unsubscribes/show.html.haml

 %h3.page-title Unsubscribe from Admin notifications
 
 %hr
-= form_tag unsubscribe_path(@email) do
+= form_tag unsubscribe_path(Base64.urlsafe_encode64(@email)) do
   %p
     Yes, I want to unsubscribe
     %strong= @email