我有同样的问题(尚未解决),但我认为它与 SpamAssassin 有关。
看起来 DKIM 签名是在 SpamAssassin 过滤器之前和之后添加的。
my mailheader
Return-Path: <info@mydomain>
X-Original-To: info@mydomain
Delivered-To: info@mydomain
Received: by mail.mydomain (Postfix, from userid 1001)
id 2D776B7CA; Wed, 7 Jun 2017 23:15:02 +0200 (CEST)
DKIM-Filter: OpenDKIM Filter v2.11.0 mail.mydomain 2D776B7CA
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mydomain;
etc.
X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on
hostname.mydomain
X-Spam-Level:
X-Spam-Status: No, score=-0.9 required=3.0 tests=ALL_TRUSTED,DKIM_SIGNED,
HTML_MESSAGE,T_DKIM_INVALID,URIBL_BLOCKED autolearn=no autolearn_force=no
version=3.4.0
Received: from [mylocalip] (myprovider [myip])
by mail.mydomain (Postfix) with ESMTPSA id BB..
for <info@mydomain>; Wed, 7 Jun 2017 23:15:01 +0200 (CEST)
DKIM-Filter: OpenDKIM Filter v2.11.0 mail.mydomain BB..
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mydomain;
etc.
猫/var/log/maillog | grep "添加了 DKIM 签名字段"
Jun 8 00:02:34 host opendkim[762]: BCD70B75A: DKIM-Signature field added (s=default, d=mydomain)
Jun 8 00:02:34 host opendkim[762]: F3341B7CA: DKIM-Signature field added (s=default, d=mydomain)
检查这个答案:
https ://serverfault.com/questions/475416/is-there-a-reason-why-dkim-signs-every-mail-twice