Email sent through CakeEmail showing attachments icon in outlook even when no attachments is sent

Question

I have using CakeEmail to send email but when I send Html and text email then the email show the attachment icon in the outlook .

I found that it is because of header Content-type: multipart/mixed; .

But it should be Content-Type:multipart/aternative;

I tried to override it by using $Email->setHeaders();

But it didn't changed.

Please suggest how do I change the Content-Type header in CakeEmail.