Form Submission Emails Vanishing

I set up a contact form to email 'enquiries@' as well as the user who has completed the form.

'Normal' email to enquiries@ (i.e. using an email client) is redirected to the two other email accounts set up. If I send a form response to enquries@ then it just disappears and is never received (the form user does get his copy).

Any idea what I'm doing wrong?

Many thanks in advance