+ * If the query goes via a CNAME then the canonical name (ie, the
+ * thing that the CNAME record refers to) is usually allowed to
+ * contain any characters, which will be quoted as above. With
+ * adns_qf_quotefail_cname you get adns_s_answerdomaininvalid when
+ * this happens. (This is a change from version 0.4 and earlier, in
+ * which failing the query was the default, and you had to say
+ * adns_qf_quoteok_cname to avoid this; that flag is now deprecated.)
+ *
+ * In version 0.4 and earlier, asking for _raw records containing
+ * mailboxes without specifying _qf_quoteok_anshost was silly. This
+ * is no longer the case. In this version only parts of responses
+ * that are actually supposed to be hostnames will be refused by
+ * default if quote-requiring characters are found.
+ */
+
+/*
+ * If you ask for an RR which contains domains which are actually
+ * encoded mailboxes, and don't ask for the _raw version, then adns
+ * returns the mailbox formatted suitably for an RFC822 recipient
+ * header field. The particular format used is that if the mailbox
+ * requires quoting according to the rules in RFC822 then the
+ * local-part is quoted in double quotes, which end at the next
+ * unescaped double quote. (\ is the escape char, and is doubled, and
+ * is used to escape only \ and ".) Otherwise the local-part is
+ * presented as-is. In any case this is followed by an @ and the
+ * domain. The domain will not contain any characters not legal in
+ * hostnames. adns will protect the application from local parts
+ * containing control characters - these appear to be legal according
+ * to RFC822 but are clearly a bad idea.
+ *
+ * If you ask for the domain with _raw then _no_ checking is done
+ * (even on the host part, regardless of adns_qf_quoteok_anshost), and
+ * you just get the domain name in master file format.
+ *
+ * If no mailbox is supplied the returned string will be `.' in either
+ * caswe.