This example shows how to send an email with attachment from Yahoo.
To send an email using Yahoo, we need to add a reference to the dynamic link library System.Net.Mail.
To do this:

• Go to solution explorer of your project
• Select add a reference
• Click on .Net Tab
• Select System.Net.Mail.

The Yahoo SMTP Server requires an encrypted connection (SSL) on port 587.

Sample :

        public void SendMailUsingYahoo()
        {
            try
            {
                MailMessage mailMessage = new MailMessage();
                mailMessage.From = new MailAddress("sender@yahoo.com");

                //receiver email adress
                mailMessage.To.Add("receiver@gmail.com");

                //subject of the email
                mailMessage.Subject = "This is a subject";

                //attach the file
                mailMessage.Attachments.Add(new Attachment(@"C:\\attachedfile.jpg"));
                mailMessage.Body = "Body of the email";
                mailMessage.IsBodyHtml = true;

                //SMTP client
                SmtpClient smtpClient = new SmtpClient("smtp.mail.yahoo.com");
                //port number for Yahoo
                smtpClient.Port = 587;
                //credentials to login in to yahoo account
                smtpClient.Credentials = new NetworkCredential("sender@yahoo.com", "password");
                //enabled SSL
                smtpClient.EnableSsl = true;
                //Send an email
                smtpClient.Send(mailMessage);
            }
            catch (Exception ex)
            {

            }
        }