I have this as a Exim4 config
dkim_domain = 3dox.org
dkim_selector = acc
dkim_private_key = /usr/share/exim4/dkim.private.key
dkim_canon = relaxed

when i send mails they are signed. BUT!!: dkim=neutral (bad format)

Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of root@3dox.org designates 176.9.148.3 as permitted sender) smtp.mail=root@3dox.org; dkim=neutral (bad format) header.i=@3dox.org
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=3dox.org; s=acc;
	h=Date:From:Message-Id:To:Subject; bh=R3/GvOej6vDO5MaZx16o/p7BTS6FxCcXFF5TIgVaRuM=;
	b=bdsz3oOpX3ge9dEuLnmVuWVaj1OHNHEbtqsRJ6dL+A2mzxFGt58ldGEv3KTtE2WKA1PpZSdo2gMjdyWYF9xgpYK7PPbMur28sgJX66i9b75qOE87UtJK1SRZZQ43d0Fu;