Remove all occurrences of dangerous email header properties from a string. This is used to prevent someone from inserting code into submitted form data that will trick the page into sending mail to other people.
E-mail header text that will be removed includes:
"x-mailer:", "x-rcpt-to:", "x-uidl:", "content-transfer-encoding:", "content-type:", "mime-version:", "x-sender:", "bcc:", "cc:", "x-receiver:"