+ dkim_sign_headers = <expanded string> [OPTIONAL]
+
+ When set, this option must expand to (or be specified as)
+ a colon-separated list of header names. These headers will
+ be included in the message signature. When unspecified,
+ the recommended headers will be used. Currently, these
+ are:
+
+ from:sender:reply-to:subject:date:
+ message-id:to:cc:mime-version:content-type:
+ content-transfer-encoding:content-id:
+ content-description:resent-date:resent-from:
+ resent-sender:resent-to:resent-cc:resent-message-id:
+ in-reply-to:references:
+ list-id:list-help:list-unsubscribe:
+ list-subscribe:list-post:list-owner:list-archive