i add only explanation for modification required for any email server to this link : Click Here
1st change :
private String mailhost = "smtp.gmail.com
change to
private String mailhost = "your smtp email server address";
2nd change :
props.put("mail.smtp.port", "465");
props.put("mail.smtp.socketFactory.port", "465");
change to
props.put("mail.smtp.port", your smtp port);
props.put("mail.smtp.socketFactory.port", your smtp port);
3rd change :
default properties are
props.setProperty("mail.transport.protocol", "smtp");
props.setProperty("mail.host", mailhost);
add more properties if your email server is required.
i hope this will help you.