Page Load and Email sending do not work when url is masked

 I have a .aspx page with a simple contact form that sends me an email.
The domain is masked and therefore points to another domain.
When you submit the contact form from the normal domain, the page refreshes properly and gives a thank you message, and the email sends.
When you submit the contact form from the masked domain, the page refreshes, the form still shows, but is all blank, and no email is sent.
Anyone know why this is happening, and how I can fix such (without un-masking the domain if possible!)
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