+ // FIXME: don't challenge emails with binaries in them;
+ // reject them outright and have the sender send an
+ // initial message w/o a binary.
+
+ // FIXME: use Auto here!!!
+ // The challenge should refer to the message-id of the mail being challenged.
+
+ // FIXME: watch outgoing MessageID's: if something comes
+ // back with an In-Reply-To mentioning a MessageID from
+ // the last few days, auto-whitelist them.
+
+ // FIXME: important that "From" on the challenge matches
+ // RCPT TO on the original message.
+