get_post () stripping (some) html

I’m modifying a plugin (post2mail) to modernize it, thinking that that would resolve the issue I’m having — namely, that while the plugin does indeed email something, it isn’t quite correct, in that p tags in post_content are gone. a tags are there, and ul and li tags, but not p. This is infuriating, as my output looks terrible. The p tags are simply gone. Is this by design? Is there some way I could make this not so? It’s so close to working the way I want it to. the code:

function post2mail($post_ID){
	global $linktext;
	require_once('post2mail.config.php');

	$the_post = get_post($post_ID, ARRAY_A);
	$subject = stripslashes($the_post['post_title']);

	/* message */
	if ($sendHTML) {
		/* To send HTML mail, you can set the Content-type header. */
		$headers  = "MIME-Version: 1.0\r\n";
		$headers .= "Content-type: text/html; charset=utf-8\r\n";
		$headers .= "Content-Transfer-Encoding: 8bit\r\n";
		$message = convert_chars($the_post['post_content']);
		$message .= addMailLinkBack($post_ID);
	}
	else {
		$headers  = "MIME-Version: 1.0\r\n";
		$headers .= "Content-type: text/plain; charset=utf-8\r\n";
		$headers .= "Content-Transfer-Encoding: 8bit\r\n";
		$message = stripslashes(strip_tags($the_post['Content']));
		$message .= "\r\n\r\n" . $linktext . ': ' . get_permalink($post_ID);
		$subject = "=?UTF-8?B?".base64_encode($subject)."?=";
	}

	/* additional headers */
	$headers .= "From: $from\r\n";
	if ($cc != '') {
		$headers .= "Cc: $cc\r\n";
	}
	if ($bcc != '') {
		$headers .= "Bcc: $bcc\r\n";
	}

	/* and now mail it */
	mail($to, $subject, $message, $headers);

	return $post_ID;
}

add_action('publish_post', 'post2mail', 5);

Any help will be enormously appreciated.