java - Could not connect to SMTP host: localhost, port: 25 -

i trying send email forgotpassword using smtp.but getting exception below

javax.mail.sendfailedexception: sending failed;   nested exception is:     class javax.mail.messagingexception: not connect smtp host: localhost, port: 25; 

the below java code

    string = email;               string = "xxxxxxx@gmail.com";                       string host = "localhost";             properties properties = system.getproperties();                 properties.setproperty("mail.smtp.host", host);                      session session = session.getdefaultinstance(properties);              try {                 mimemessage message = new mimemessage(session);                              message.setfrom(new internetaddress(from));                 message.addrecipient(message.recipienttype.to, new internetaddress(                         to));                 message.setsubject("this subject line!");                 message.setcontent("<h1>this actual message</h1>", "text/html");                 transport.send(message); } 

can 1 please tell me how can send email using smtp