Double Opt-In setup not working on host site.

I have followed the double opt-in system set up tutorial and it works perfectly on my localhost setup using XAMPP the mail works both ways using Mercury32. However, when I transfer it to the online host site and establish the connection whereby the scripts can read the database, however when it comes to sending the verification email out it stops working and the email doesn't get sent.

I checked with my provider and they have a document which I have copied here:


To prevent spam being sent through our webservers, there are certain conditions that must be met before our SMTP servers will send the email.

Email must be sent to, or from, an existing email address hosted by Fasthosts. This must be a mailbox on the same domain name on which the form to mail script is being hosted.
To stop misuse of your form by third parties the sendmail_from variable should be set to your Fasthosts hosted email address. While access to the php.ini file is restricted on our shared environment, you can sent this variable using the ini_set() command, shown below.
A fifth parameter, -f, should be added to the sendmail function. This will set the name of the from email address.

Having looked at the associated pages created by Data Bridge during the tutorial I see that the following files already have the -f switch already:

webassist\email\mail_php.php - $mailObj = @mail($mailTo,$mailSubject,$mailContent,$mailHeader,"-f".$mailFrom." -r".$mailObj->ReturnPath);
webassist\security_assist\mail_php.php - $mailObj = @mail($mailTo,$mailSubject,$mailContent,$mailHeader,"-f".$mailFrom." -r".$mailObj->ReturnPath);

is there anywhere else I need to put it? Has anyone else had this problem?

I have also made sure that the $MailFrom has a Fasthosts email address.

Appreciate any help, I have been pulling out my hair on this and talking with the Fasthost technician is even more of a frustration as they don't seem to understand their own restrictions.