More and more providers change the rules for how they accept mails from their clients. SMTP on port 25 is reserved for communication with other systems (i.e. to deliver mails to the provider's clients), clients should deliver their mails to port 587 (submission service) to send mail.

Try changing $port = 25; to $port = 587;. This may give you the same results, because usually the port 587 requires a login, too. Try contacting the ipower support for mail delivery account name and password.

Alexander