diff --git a/doc/release-notes.md b/doc/release-notes.md
--- a/doc/release-notes.md
+++ b/doc/release-notes.md
@@ -76,3 +76,27 @@
 ------------
 
 - `createwallet` can now create encrypted wallets if a non-empty passphrase is specified.
+
+
+Configuration
+-------------
+
+The outbound message high water mark of the ZMQ PUB sockets are now
+configurable via the options:
+
+`-zmqpubhashtxhwm=n`
+
+`-zmqpubhashblockhwm=n`
+
+`-zmqpubrawblockhwm=n`
+
+`-zmqpubrawtxhwm=n`
+
+Each high water mark value must be an integer greater than or equal to 0.
+The high water mark limits the maximum number of messages that ZMQ will
+queue in memory for any single subscriber. A value of 0 means no limit.
+When not specified, the default value continues to be 1000.
+When a ZMQ PUB socket reaches its high water mark for a subscriber, then
+additional messages to the subscriber are dropped until the number of
+queued messages again falls below the high water mark value.
+