+PH/29 After an address error (typically a 4xx response from a server), Exim
+ always tries the failing address if it appears in a new message, but
+ respects the retry time otherwise. This was implemented by checking for
+ being in a queue run, which isn't quite right. Now it checks the
+ "first_delivery" flag instead.
+
+PH/30 Exim was sometimes attempting to deliver messages that had suffered
+ address errors (4xx response to RCPT) over the same connection as other
+ messages routed to the same hosts. Such deliveries are always "forced",
+ so retry times are not inspected. This resulted in far too many retries
+ for the affected addresses. The effect occurred only when there were more
+ hosts than the hosts_max_try setting in the smtp transport when it had
+ the 4xx errors. Those hosts that it had tried were not added to the list
+ of hosts for which the message was waiting, so if all were tried, there
+ was no problem. Two fixes have been applied:
+
+ (i) If there are any address or message errors in an SMTP delivery, none
+ of the hosts (tried or untried) are now added to the list of hosts
+ for which the message is waiting, so the message should not be a
+ candidate for sending over the same connection that was used for a
+ successful delivery of some other message. This seems entirely
+ reasonable: after all the message is NOT "waiting for some host".
+ This is so "obvious" that I'm not sure why it wasn't done
+ previously. Hope I haven't missed anything, but it can't do any
+ harm, as the worst effect is to miss an optimization.
+
+ (ii) If, despite (i), such a delivery is accidentally attempted, the
+ routing retry time is respected, so at least it doesn't keep
+ hammering the server.
+