codeigniter mail sending error 451

Can any one tell me why I'm getting this error with codeigniter when it comes to sending开发者_如何转开发 mail.

some time it work fine some times i get this error

451 Please try again later The following SMTP error was encountered: 451 Please try again later Unable to send email using PHP SMTP. Your server might not be configured to send mail using this method.

Are you sure your SMTP server is working fine at the time you get this error? If it works sometimes, then that means that your configuration is probably fine. I'd deploy the code of a test server online and then run your code to see if its really a configuration problem or maybe a problem with the SMTP host that you're trying to send the mail through.