Check Email using RegEx class.

using System.Text.RegularExpressions;
private const string _iPattern = @"^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$";

public bool CheckEmailAddress(string EmailAddress)
    {
        bool Check = false;

        Regex RegEx = new Regex(_iPattern);
        Check = RegEx.IsMatch(EmailAddress);
        return Check;
    }

bool is_valid_email_id1 = CheckEmailAddress("abc@xyz.com"); //true 
bool is_valid_email_id2 = CheckEmailAddress("abcxyz.com");  //false 
bool is_valid_email_id3 = CheckEmailAddress("a@bcxyz");     //false