c# - SMTP mail errors -

i developing c# application send mail using smtp server of our company mail. following code.

mailmessage mail = new mailmessage(); smtpclient smtpserver = new smtpclient("10.203.195.48");  mail.from = new mailaddress(""); mail.to.add(""); mail.subject = "filename"; mail.body = "report";  smtpserver.host = "ip address fo smtp mail server."; smtpserver.port = 25; smtpserver.credentials = new system.net.networkcredential("", "");  smtpserver.send(mail); 

but error:

mailbox unavailable.unable relay.the system doesn't have internet connection.

the following code gmail smtp using port 587. change port , smtp.

add namespace

using system.net mailmessage mymailmessage = new mailmessage(); mymailmessage.from = new mailaddress("emailid"); mymailmessage.to.add("to"); mymailmessage.subject = "feedback form"; mymailmessage.body = "this test message"; mymailmessage.isbodyhtml = true;  smtpclient smtpserver = new smtpclient("smtp.gmail.com"); smtpserver.port = 587; smtpserver.credentials = new system.net.networkcredential("username","password"); smtpserver.enablessl = true;  try {     smtpserver.send(mymailmessage); }  catch (exception ex) {     ex.message("error"); }