Invite friend not working

Hi I installed DC on my server but the invite friend is not sending any invite. I contacted my hosting provider and they told me this 

Thank you for contacting our Technical Support Department.

To be able to send a script generated mail through the server you have to set either the recipient's e-mail address (the "To:" header) or the sender's e-mail address (the "From:" header) to be an e-mail address from your hosted domain on the server.

Could you please check your script configuration so it meats this requirement?

 

Anybody bodies know how to make these modifications?

Thanks