Two possibilities: Include your IP in the SPF or send via user/pass authenticated SMTP service (gmail, hotmail, etc). Your postfix can be configured to route mails to a "forwarding" smtp service instead of direct to the destination. No changes to your script, just to the postfix email system (or exim, or sendmail, whichever your system is using).
We ordinarily charge $99 to set all that up, but is seems you'll be likely able to do it on your own.