unable to send mail mail getting error as

System.Net.Mail.SmtpException: User not local; please try a different path. The server response was: Sender address is not valid for your login. Check your email program settings. at System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response) at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, MailAddress from, Boolean allowUnicode) at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception) at System.Net.Mail.SmtpClient.Send(MailMessage message) at MasterPage.Button1_Click(Object sender, EventArgs e) in c:\inetpub\vhosts\aasthagroup.co.in\httpdocs\MasterPage.master.cs:line 37