Mailgate whitelisting

[film.psychos]

Hi I've got a form on one of my websites that gets a user to fill out
a form and sents it to my gmail email account, comes with following error message when I test it out:
The recipient address is unknown
The address you are trying to send to ([email address],) is not
authorized to receive mail via this gateway.


Please contact the webmaster of the page that referred you to this
link and inform them they will no longer be able to use this function
to send mail to [email address],.

If you feel this error is incorrect and that you should be able to
send mail via this gateway, please contact the ISP that referred you
to the mailgate service.


Is there some setting that I could put to allow this funciton to work? or how would I go about this.
Thanks in advance.