Add tests for invalid domains, probably not a security issue in the DKIM context, but we should raise errors here.

dkim/tests/data/test.message.baddomain

@@ -0,0 +1,16 @@
+DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple;
+ d=legitimate.com(.attacker.com; [email protected](.attacker.com;
+ q=dns/txt; s=test; t=1587514615; h=message-id : date : from : to :
+ subject : from; bh=wE7NXSkgnx9PGiavN4OZhJztvkqPDlemV3OGuEnLwNo=;
+ b=LsTV4fcR29N8CuUyrGn92jsTb67oAHx88vVIefoaUDghWxF5TpCyqcWbk/94Nt4PyxwUZ
+ pgzF4UM/zF1rclCeNm/V4m0wMj3X2eeOIUUa8GRQ0g7DzixiQ5qHLUGpRT4BHfPmdHZHYj8
+ xv7+1O0/SJDK0YkaBjvhjDfkOoJhMmc=
+Authentication-Results: lists.example.org; arc=none; spf=pass [email protected]; dkim=pass (1024-bit key) [email protected]; dmarc=pass
+Received: from localhost
+Message-ID: <[email protected]>
+Date: Mon, 01 Jan 2011 01:02:03 +0400
+From: Test User <[email protected]>
+To: [email protected]
+Subject: Testing
+
+This is a test message.