Unable to send mail from server

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C#

.NET

I am sending mails using my live account and my code works fine on localhost but gives an exception on server:
Mailbox unavailable. The server response was: 5.7.3
Requested action aborted; user not authenticated
Below is my code:

public static string SendEmail(string receivermailid, string subject, string body)
    {
        
        MailMessage MyMailMessage = new MailMessage("xyz@live.com", receivermailid, subject, body);
        MyMailMessage.IsBodyHtml = true;
        NetworkCredential mailAuthentication = new
        NetworkCredential("xyz@live.com", "xxxx");
        SmtpClient mailclient = new SmtpClient("smtp.live.com", 25);
        mailclient.EnableSsl = true;
        mailclient.UseDefaultCredentials = false;
        mailclient.Credentials = mailAuthentication;
        try
        {
            mailclient.Send(MyMailMessage);

            return "Sent successfully";
        }
        catch (SmtpException ex)
        {
            return ex.Message;
        }