.netCore email verify before seding - asp.net-core

Question

I'm looking for a method to validate the email address before sending. On email dns server.
I do NOT need regex or form email validation.
If user inputs test#google.com I want to know if there is an address like this on google server. I know there are some products that do the email validation. But we do not have money for that.
I'm using .netCore mailkit as smptClient. I've saw that there is a verify method but it somehow does the call but never returns.
Can you help please?

Answer 1

The only way to validate an email address is to send an email to that address with a link the user must click. That link should have a token uniquely generated for the user. Your site, then, looks up the token from the user when the user visits your site with that link and marks the associated user's email as verified.
If you're using Identity, support for this is baked in. There's a tutorial in the Microsoft docs. Essentially, it involves just adding a line in your AddIdentity config in Startup.cs:
config.SignIn.RequireConfirmedEmail = true;
Then, in your register action, you'd use the following to generate the URL for the link in the confirmation email:
var code = await _userManager.GenerateEmailConfirmationTokenAsync(user);
var callbackUrl = Url.EmailConfirmationLink(user.Id, code, Request.Scheme);
Next, just send the email to the user in any way you like. In your email confirmation action, the following confirms the email based on the code in the URL:
var result = await _userManager.ConfirmEmailAsync(user, code);
EDIT
The Url.EmailConfirmationLink method actually comes from an extension added in the generated code when you add individual auth to a new project. Here's the code for that, for reference:
public static string EmailConfirmationLink(this IUrlHelper urlHelper, string userId, string code, string scheme)
{
return urlHelper.Action(
action: nameof(AccountController.ConfirmEmail),
controller: "Account",
values: new { userId, code },
protocol: scheme);
}