In this article I will explain with an example, how to perform Server Side Email validation using Data Annotation attribute in ASP.Net Core MVC.
The Server Side Email validation will be performed using Model class and Data Annotation attributes.
The following Model class consists of one property Email. The property is decorated with the following Data Annotation attributes for performing validations.
1. Required Data Annotation attribute.
2. EmailAddress Data Annotation attribute.
The Data Annotations attributes can be used with the Entity Data Model (EDM), LINQ to SQL, and other data models.
The Required Data Annotation and the EmailAddress Data Annotation attributes have been specified with a property Error Message with a string value. As the name suggests, this string value will be displayed to the user when the respective validation fails.
using System.ComponentModel.DataAnnotations;
namespace Email_Validation_Server_Side_MVC_Core.Models
    public class PersonModel
        [Required(ErrorMessage = "Email is required.")]
        [EmailAddress(ErrorMessage = "Invalid Email Address.")]
        public string Email { get; set; }
The Controller consists of following two Action methods.
Action method for handling GET operation
Inside this Action method, simply the View is returned.
Action method for handling POST operation
This Action method handles the POST operation and when the form is submitted, the object of the PersonModel class is sent to this method.
The state of the submitted Model is checked using ModelState.IsValid property.
Note: ModelState.IsValid property is an inbuilt property which verifies two things:
1. Whether the Form values are bound to the Model.
2. All the validations specified inside Model class using Data annotations have been passed.
public class HomeController : Controller
    public IActionResult Index()
        return View();
    public IActionResult Index(PersonModel person)
        if (ModelState.IsValid)
            // Validation success.
        return View();
Inside the View, in the very first line the PersonModel class is declared as Model for the View.
The Form
The View consists of an HTML Form which has been created using following ASP.Net Tag Helpers attributes.
asp-action – Name of the Action. In this case the name is Index.
asp-controller – Name of the Controller. In this case the name is Home.
method – It specifies the Form Method i.e. GET or POST. In this case it will be set to POST.
The Form consists of a HTML INPUT TextBox, a SPAN element and a Submit Button.
The INPUT TextBox has been assigned with asp-for Tag Helper attribute and its value is set with the Email property. Thus, this signifies that the validation will be performed for the Email property.
The SPAN has been assigned with asp-validation-for Tag Helper attribute and here also its value is set with the Email property which signifies that it is used for displaying the Validation message for the Email property.
When the Submit button is clicked, the Form gets submitted and the Email value is sent to the Controller.
@model Email_Validation_Server_Side_MVC_Core.Models.PersonModel
@addTagHelper*, Microsoft.AspNetCore.Mvc.TagHelpers
    Layout = null;
<!DOCTYPE html>
    <meta name="viewport" content="width=device-width" />
    <style type="text/css">
        body { font-family: Arial; font-size: 10pt; }
        .error { color: red; }
    <form method="post" asp-controller="Home" asp-action="Index">
                <td><input type="text" asp-for="Email" /></td>
                <td><span asp-validation-for="Email" class="error"></span></td>
                <td><input type="submit" value="Submit" /></td>
ASP.Net Core MVC: Server Side Email Validation using Data Annotation attributes