Email id validation

In the new user registration page, how to check whether the email id entered by a user is valid? I want to check the entered email id actually 开发者_运维技巧exists before the user submits his information. Please do not give code for checking email id string using regular expression, I want to check whether the entered email id actually exists.

You can not "check" that reliably. You need to "ask", send an email to that address with a secret code that your users must enter on your site, or a link with the secret code that the user must click.

Edit: About the reliably part.
While an SMTP server may respond that a mail address is invalid they usually don't, because that would help spammers identify valid addresses more easily. That would also require your code to talk directly to the SMTP servers responsible for each domain. Usually you send mail though your local SMTP server that does the job of forwarding the mail to the right recipient(s).

What you can do however is at least check that the domain exists by asking your favorite DNS service.

In order to do this, you'd need to telnet to the email provider in order to check if it exists. Hotmail, for one, will not allow you to do this.

You should be using membership system for your ASP.net registration form.

Here is a good article explaining how it all works:

https://web.archive.org/web/20211020202857/http://www.4guysfromrolla.com/articles/120705-1.aspx

Including a page on how to verify email addresses like you describe

The only 100% accurate method is to send it an email and ask the user to click a link in that email to complete registration.

Short of that, there is a falible method of connecting to the mailserver. I'll see if I can find a good article(here you go) and edit this post with a link shortly.

This depends on the email provider. most of the providers block this option to prevent spammers from knowing which address is valid...