Get cron to send html-formatted emails

I put the CONTENT_TYPE="text/plain; charset=utf-8" in /etc/crontab to have my mail in UTF-8.

Put CONTENT_TYPE="text/html; charset=utf-8" in /etc/crontab to send the mail in HTML.

You may add it in specific file if the directory /etc/cron.d/ exists. In this case, the specification is defined only for the requested tasks.

I don't think you can. A solution could be to pipe the output to sendmail or mail, which gives you more control over content type and other headers.