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diff --git a/docs/upgrade.md b/docs/upgrade.md
index 312f0b87fe..3aaeb499ce 100644
--- a/docs/upgrade.md
+++ b/docs/upgrade.md
@@ -89,6 +89,21 @@ process, for example:
     dpkg -i matrix-synapse-py3_1.3.0+stretch1_amd64.deb
     ```
 
+# Upgrading to v1.64.0
+
+## Delegation of email validation no longer supported
+
+As of this version, Synapse no longer allows the tasks of verifying email address
+ownership, and password reset confirmation, to be delegated to an identity server.
+
+To continue to allow users to add email addresses to their homeserver accounts,
+and perform password resets, make sure that Synapse is configured with a
+working email server in the `email` configuration section (including, at a
+minimum, a `notif_from` setting.)
+
+Specifying an `email` setting under `account_threepid_delegates` will now cause
+an error at startup.
+
 # Upgrading to v1.62.0
 
 ## New signatures for spam checker callbacks