+// FIXME: bounce messages (must go to return-path unless empty, in which case do not send
+// FIXME: if more than 100 "Received" lines, must drop message
+// FEATURE: infer messageid, date, if not present (?)
+// FEATURE: RFC2822, section 4.5.1: special "postmaster" address
+// FEATURE: RFC2822, section 4.5.4.1: retry strategies
+// FEATURE: RFC2822, section 5, multiple MX records, preferences, ordering