Doc: add clarification for DKIM example

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index dfbd7e6e90008deb426ad6ec660ba60d7f56bf06..54775aecd01c1bffb586bcb42168ba6810f47e5d 100644 (file)
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -38379,13 +38379,18 @@ for a match against the domain or identity that the ACL is currently verifying
 verb to a group of domains or identities. For example:
 
 .code
-# Warn when Mail purportedly from GMail has no signature at all
-warn log_message = GMail sender without DKIM signature
+# Warn when Mail purportedly from GMail has no gmail signature
+warn log_message = GMail sender without gmail.com DKIM signature
      sender_domains = gmail.com
      dkim_signers = gmail.com
      dkim_status = none
 .endd
 
+.new
+Note that the above does not check for a total lack of DKIM signing;
+for that check for empty &$h_DKIM-Signature:$& in the data ACL.
+.wen
+
 .vitem &%dkim_status%&
 ACL condition that checks a colon-separated list of possible DKIM verification
 results against the actual result of verification. This is typically used