send mail with asp.net

Try this,

MailMessage msgMail = new MailMessage();
SmtpClient smtp = new SmtpClient("servername", "portno");
msgMail.From = new MailAddress("fromaddress", "from name");
msgMail.To.Add(new MailAddress("toaddress"));

msgMail.Subject = "Subject";
msgMail.Body = "Body";
smtp.Send(msgMail);

It can be because of various reasons. You need to look at them one by one.
Is the port open? Firewall permissions in place?
Further make sure you have configured SMTP configuration in Web.Config:

<system.net>
   <mailSettings>
     <smtp from="abc@somedomain.com">
       <network host="somesmtpserver" port="25" userName="name" password="pass" defaultCredentials="true" />
     </smtp>
   </mailSettings>
</system.net>

If needed, have a look at this Microsoft Video tutorial:
Use ASP.NET to send Email from Website[^]

Please try this one..

public void SendMail(string to, string subject, string body
            , string mailUserName, string mailPassword
            , string smtpHost, string mailFrom, bool isBodyHtml
            , int smtpPort, bool enableSSL)
        {
            MailMessage mailMsg = new MailMessage();
            mailMsg.From = new MailAddress(mailFrom);
            mailMsg.To.Add(to);
            mailMsg.Subject = subject;
            mailMsg.IsBodyHtml = true;
            mailMsg.BodyEncoding = Encoding.UTF8;
            mailMsg.Body = body;
            mailMsg.Priority = MailPriority.Normal;
            // Smtp configuration
            SmtpClient client = new SmtpClient();
            client.Credentials = new NetworkCredential(mailUserName, mailPassword);
            client.Port = smtpPort;
                 
            client.Host = smtpHost;
            client.EnableSsl = enableSSL;
            try
            {
                client.Send(mailMsg);
            }
            catch (SmtpException smtpException)
            {
                throw smtpException;
            }
        }

You may set the username, password etc by reading from the configuration file