在C＃中检查有效的电子邮件地址

Question

I'm sending email using smtp services in my c# windows application. I have to perform in a best way to reduce the email bounce rate. I have to check the provided email address is valid or not. I'm using the code.

    private void btnCheckValid_Click(object sender, EventArgs e)
        {
            if (isRealDomain(textBox1.Text.Trim()) == true)
                MessageBox.Show("Valid Email Address!");
        }
        private bool isRealDomain(string inputEmail)
        {
            bool isReal = false;
            try
            {
                string[] host = (inputEmail.Split('@'));
                string hostname = host[1];

                IPHostEntry IPhst = Dns.GetHostEntry(hostname);
                IPEndPoint endPt = new IPEndPoint(IPhst.AddressList[0], 25);
                Socket s = new Socket(endPt.AddressFamily,
                        SocketType.Stream, ProtocolType.Tcp);
                s.Connect(endPt);
                s.Close();
                isReal = true;
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
                isReal = false;
            }

            return isReal;
        }

By checking the real domain I can identified the Hosted IP but the email address is created on the host or not.

with regex (regular expression ) I can valid only format.

So my question is how to find only valid address of any domain in c#.

Answer 1

You can import System.ComponentModel.DataAnnotations and use it in this way:

private bool validMail(string address)
{
    EmailAddressAttribute e = new EmailAddressAttribute();
    if (e.IsValid(address))
        return true;
    else
        return false;
}

Answer 2

You can use regular expressions like:

    public static bool IsValidEmailAddress(string emailaddress)
    {
        try
        {
            Regex rx = new Regex(
        @"^[-!#$%&'*+/0-9=?A-Z^_a-z{|}~](\.?[-!#$%&'*+/0-9=?A-Z^_a-z{|}~])*@[a-zA-Z](-?[a-zA-Z0-9])*(\.[a-zA-Z](-?[a-zA-Z0-9])*)+$");
            return rx.IsMatch(emailaddress);
        }
        catch (FormatException)
        {
            return false;
      }
}

UPDATE:

If you want to validate for a specific domain as you said in comments its even simpler:

Regex rx = new Regex(
@"^[-!#$%&'*+/0-9=?A-Z^_a-z{|}~](\.?[-!#$%&'*+/0-9=?A-Z^_a-z{|}~])*@yourdomain.com$");

Replace yourdomain.com with your domain name.

Answer 3

Using the .Net mail namespace you can verify email address like this:

using System.Net.Mail;

private bool EmailVerify(string email)

    {
        try
        {
            var mail = new MailAddress(email);

            return mail.Host.Contains(".");
        }
        catch
        {
            return false;
        }
    }

Answer 4

If you are using

System.Net.Mail.SmtpClient

The most accurate way I've found is to attempt to create a

System.Net.Mail.MailAddress

object. If you cannot create the object with the address in your string it will throw one of the following:

ArgumentNullException // The address is null
ArgumentException // The address is string.Empty
FormatException // The address is not in a recognized format

https://msdn.microsoft.com/en-us/library/591bk9e8(v=vs.110).aspx

I've found that

Dns.GetHostEntry

is iffy at best. It does not seem to recognize multilayered domains as valid (domain.subdomain1.subdomain2.com), so checking the domain using that method is NOT definitive.

Using a RegEx is ok, but they often fail to recognize quoted addresses and other valid patterns (which are fine according to the RFC) as valid.

Since, to use the SmtpClient class you have to have a valid MailAddress object anyway, it just makes sense.

Answer 5

Here is an another way to check valid email address

 public bool IsValidEmail(string email)
    {
        try
        {
            var addr = new System.Net.Mail.MailAddress(email);
            return addr.Address == email;
        }
        catch
        {
            return false;
        }
    }

Answer 6

 public static bool IsValidEmail(string emailaddress)
    {
           return new EmailAddressAttribute().IsValid(emailaddress);
    }
// using System.ComponentModel.DataAnnotations;