Is it just to make sure that the user inputs something other than rubbish?Obviously there are expressions that you could use to determine if the format of an e-mail address is valid but you can also use the System.If it retrieves the recipient’s local SMTP server successfully, Smtp Client will try to connect to this server.Smtp Client then performs “RCPT TO” command to test if this SMTP server accepts this email address.
Another important point to consider is that do you need to be performing this?
For example, it will fail to validate "Bob Bobson TIP: Keep in mind that almost any character is legal in an email address if it is properly quoted, so if you are passing an email address to something that may be sensitive to certain characters or character sequences (such as a command shell), you must be sure to properly escape those characters.
Email Checker is a simple tool for verifying an email address. It extracts the MX records from the email address and connect to mail server (over SMTP and also simulates sending a message) to make sure the mailbox really exist for that user/address.
Then it tells you whether the email address is real or not.
Some mail servers do not co-operate in the process, in such cases, the result of this email verification tool may not be as accurate as expected.