You can add additional mail headers to the emails sent by your contact forms in the Additional Headers Section of the Mail Tab for either Mail or Mail(2).
There should be only one field per line. Mail Tags can be embedded in the fields.
Note: For DMARC-compliance, the default mail template sets the “From” email to an email address on your domain, and adds a Reply-To entry in the Additional Headers section so that you can reply to the submitter when you receive the email from the contact form.
CC and BCC Headers
You can add a CC or BCC to your contact form emails by adding a line like the following in the Additional Headers Section: