Send mail with attachment CSV showing base64 format

When i send CSV attachment in mail, showing base64 format in mail response

Mail::send('emails.waitingTime', [], function ($message) use ($email, $subject, $fileName) {
    $message->to($email)->subject($subject)->attach(URL::asset('/'. $fileName))->setContentType('text/csv');
});

Showing in mail

--_=_swift_1574330801_b65df1604759f4a281a1fd4aab1b757b_=_ Content-Type: text/csv; name=unifonmitel.csv Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename=unifonmitel.csv TGlzdGVkLCBBdmcgd2FpdGluZyB0aW1lCkt1bmRlc3VwcG9ydCwgNi43NjU2MjUKU2FsZ3NzdXBw b3J0LCA1LjUKSVQgU3VwcG9ydCwgMi4yCg== --_=_swift_1574330801_b65df1604759f4a281a1fd4aab1b757b_=_--

via Chebli Mohamed