smtp helo command and email address used

Hi

I have written a php script that sends an email. I have specified the correct from address and to address but the email address gets rejected by the recipients spam filter. When I examine the reply from the other mail server the helo command that my web server runs to connect to the recipient uses an email address which is linuxusername@domain.com - ozonesco@web1.origination.net in this case. I believe this is why the email is bouncing - what I would like to do is to change this address to noreply@ozones.co.uk

Can anyone advise on how I can do this

Nick