/**
 * Filter the mail content type.
 */
function wpdocs_set_html_mail_content_type() {
	return 'text/html';
}
add_filter( 'wp_mail_content_type', 'wpdocs_set_html_mail_content_type' );

$to      = 'sendto@example.com';
$subject = 'The subject';
$body    = 'The email body content';

wp_mail( $to, $subject, $body );

// Reset content-type to avoid conflicts -- https://core.trac.wordpress.org/ticket/23578
remove_filter( 'wp_mail_content_type', 'wpdocs_set_html_mail_content_type' );