sendmail.cf content-type block

It is possible to configure sendmail to block based on the MIME "Content-type:" header. i generally don't like receiving HTML email, so i came up with the following 'sendmail.cf' changes to bounce such email. i've found that this also seems to have the added benefit of bouncing a lot of spam.
The preferred method would be to change the .mc file and use that to generate the .cf file.

sendmail.mc additions

Add the following to the .mc file and regenerate the .cf file.

         LOCAL_RULESETS
	 HContent-type: $>CheckContentType

	 SCheckContentType
	 Rtext/html$*    $#error $: 553 We speak English,\ not HTML

sendmail.cf additions

If you don't have a .mc file corresponding to your .cf file, then you can add the following to the .cf file.

         HContent-type: $>CheckContentType

	 SCheckContentType
	 Rtext/html$*	$#error $: 553 We speak English,\ not HTML