- * 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.
+ * unescaped double quote (\ is the escape char, and is doubled, and
+ * is used to escape only \ and "). If the local-part is legal
+ * without quoting according to RFC822, it is presented as-is. In any
+ * case the local-part is followed by an @ and the domain. The domain
+ * will not contain any characters not legal in hostnames.
+ *
+ * Unquoted local-parts may contain any printing 7-bit ASCII
+ * except the punctuation characters ( ) < > @ , ; : \ " [ ]
+ * I.e. they may contain alphanumerics, and the following
+ * punctuation characters: ! # % ^ & * - _ = + { } .
+ *
+ * adns will reject local parts containing control characters (byte
+ * values 0-31, 127-159, and 255) - these appear to be legal according
+ * to RFC822 but are clearly a bad idea. RFC1035 syntax does not make
+ * any distinction between a single RFC822 quoted-string containing
+ * full stops, and a series of quoted-strings separated by full stops;
+ * adns will return anything that isn't all valid atoms as a single
+ * quoted-string. RFC822 does not allow high-bit-set characters at
+ * all, but adns does allow them in local-parts, treating them as
+ * needing quoting.