docs: update for multi-recipient changes

docs/changelog/main.md

@@ -2,6 +2,18 @@
 
 ## Breaking Changes
 
+ * Enabling
+   [`batch_handling="BatchByDomain"`](../reference/kumo/start_esmtp_listener/batch_handling.md)
+   will cause [message:recipient](../reference/message/recipient.md) and the
+   `recipient` field of [Log Record](../reference/log_record.md) to switch to
+   an array holding the list of recipients.  These are *NOT* active by default,
+   but if you wish to enable them you should audit your policy and consider
+   switching to using
+   [message:recipient_list](../reference/message/recipient_list.md) as well as
+   review your log processors to ensure that they are able to handle the
+   `recipient` field being either an array or a string, or otherwise adjusting
+   your log templates accordingly.
+
 ## Other Changes and Enhancements
 
  * [msg:check_fix_conformance](../reference/message/check_fix_conformance.md#fixing-8-bit-content)

docs/reference/log_record.md

@@ -22,6 +22,10 @@ The log record is a JSON object with the following shape:
     "sender": "user@sender.example.com",
 
     // The envelope recipient
+    //
+    // If the message has multiple recipients (eg: it was part of
+    // an SMTP batch transaction) this will be an array of the
+    // recipients. (Multi-recipient is possible {{since('dev', inline=True)}})
     "recipient": "user@recipient.example.com",
 
     // Which named queue the message was associated with