How do I send mail to all mail extensions?

Question

I am trying to send an e-mail to the e-mail address entered in the textbox1.text field. I have no problems sending e-mail to Hotmail, but I get an error when trying to send e-mail to Gmail. I'm using this code to send email.

    string to = Textbox1.Text;
    string subject = "Mail subject";
    string body = "Hello";
    
    string fromAddress = "test@hotmail.com";
    string password = "xyz";
    
    string smtpServer;
    int smtpPort;
    bool enableSSL;
    
    string domain = to.Substring(to.IndexOf("@") + 1);
    
    switch (domain.ToLower())
    {
        case "gmail.com":
            smtpServer = "smtp.gmail.com";
            smtpPort = 587;
            enableSSL = true;
            break;
        case "hotmail.com":
            smtpServer = "smtp.office365.com";
            smtpPort = 587;
            enableSSL = true;
            break;
        default:
            MessageBox.Show("The specified email provider is not supported.");
            return;
    }
    
    SmtpClient smtpClient = new SmtpClient(smtpServer);
    smtpClient.Port = smtpPort;
    smtpClient.Credentials = new NetworkCredential(fromAddress, password);
    smtpClient.EnableSsl = enableSSL;
    
    MailMessage mailMessage = new MailMessage(fromAddress, to, subject, body);
    smtpClient.Send(mailMessage);

The text below shows the error I get when trying to send an e-mail.

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Authentication Required. Learn more at

Answer 1

change your code like this;

string to = Textbox1.Text;
string subject = "Mail subject";
string body = "Hello";

string fromAddress = "test@hotmail.com";
string password = "xyz";

string smtpServer;
int smtpPort;
bool enableSSL;
smtpServer = "smtp.office365.com";
smtpPort = 587;
enableSSL = true;

SmtpClient smtpClient = new SmtpClient(smtpServer);
smtpClient.Port = smtpPort;
smtpClient.Credentials = new NetworkCredential(fromAddress, password);
smtpClient.EnableSsl = enableSSL;

MailMessage mailMessage = new MailMessage(fromAddress, to, subject, body);
smtpClient.Send(mailMessage);