This function allows sending of emails with correct handling of Cc and Bcc receivers.
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.