----------
Send Email from Yahoo!, GMail, Hotmail (C#)

Server Parameters 
Server Name SMTP Address Port SSL 
Yahoo! smtp.mail.yahoo.com 587 Yes 
GMail smtp.gmail.com 587 Yes 
Hotmail smtp.live.com 587 Yes 


using System.Net;
using System.Net.Mail;

string smtpAddress = "smtp.mail.yahoo.com";
int portNumber = 587;
bool enableSSL = true;

string emailFrom = "email@yahoo.com";
string password = "abcdefg";
string emailTo = "someone@domain.com";
string subject = "Hello";
string body = "Hello, I'm just writing this to say Hi!";

using (MailMessage mail = new MailMessage())
{
    mail.From = new MailAddress(emailFrom);
    mail.To.Add(emailTo);
    mail.Subject = subject;
    mail.Body = body;
    mail.IsBodyHtml = true;
    // Can set to false, if you are sending pure text.

    mail.Attachments.Add(new Attachment("C:\\SomeFile.txt"));
    mail.Attachments.Add(new Attachment("C:\\SomeZip.zip"));

    using (SmtpClient smtp = new SmtpClient(smtpAddress, portNumber))
    {
        smtp.Credentials = new NetworkCredential(emailFrom, password);
        smtp.EnableSsl = enableSSL;
        smtp.Send(mail);
    }
}

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//Short Method
try
{
    SmtpClient smtp = new SmtpClient("smtp.gmail.com", 587);
    smtp.UseDefaultCredentials = false;
    smtp.Credentials = new NetworkCredential("username", "password");
    smtp.EnableSsl = true;
    smtp.Send("sender@gamil.com", "receiver", "subject", "Email Body");
}
catch(Exception ex)
{
    Console.WriteLine(ex.Message);
}

----------
//Detailed Method
try
{
    MailAddress mailfrom = new MailAddress("sender@gmail.com");
    MailAddress mailto = new MailAddress("receiver@abc.com");
    MailMessage newmsg = new MailMessage(mailfrom, mailto);

    newmsg.Subject = "Subject of Email";
    newmsg.Body = "Body(message) of email";

    //For File Attachment, more file can also be attached
    Attachment att = new Attachment("C:\\...file path");
    newmsg.Attachments.Add(att);

    SmtpClient smtp = new SmtpClient("smtp.gmail.com", 587);
    smtp.UseDefaultCredentials = false;
    smtp.Credentials = new NetworkCredential("username","password");
    smtp.EnableSsl = true;
    smtp.Send(newmsg);    
} 
catch(Exception ex)
{
    Console.WriteLine(ex.Message);
}