This function allows sending of emails with correct handling of Cc and Bcc receivers.
The parameters to, cc and bcc are all strings and are all parsed as » RFC822 address lists.
The mail subject
The mail body
As string with additional headers to be set on the mail
The receivers specified in bcc will get the mail, but are excluded from the headers.
Use this parameter to specify return path upon mail delivery failure. This is useful when using PHP as a mail client for multiple users.