attach($filename[, $disposition = ''[, $newname = NULL[, $mime = '']]]) 
Parameters:
$filename (string) – File name 
$disposition (string) – ‘disposition’ of the attachment. Most email clients make their own decision regardless of the MIME specification used here. https://www.iana.org/assignments/cont-disp/cont-disp.xhtml
 
$newname (string) – Custom file name to use in the e-mail 
$mime (string) – MIME type to use (useful for buffered data)  Returns:
CI_Email instance (method chaining)  R