diff --git a/INSTALL.md b/INSTALL.md
index 69e423923b..e7b429c05d 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -413,16 +413,18 @@ For a more detailed guide to configuring your server for federation, see
 
 ## Email
 
-It is desirable for Synapse to have the capability to send email. For example,
-this is required to support the 'password reset' feature.
+It is desirable for Synapse to have the capability to send email. This allows
+Synapse to send password reset emails, send verifications when an email address
+is added to a user's account, and send email notifications to users when they
+receive new messages.
 
 To configure an SMTP server for Synapse, modify the configuration section
-headed ``email``, and be sure to have at least the ``smtp_host``, ``smtp_port``
-and ``notif_from`` fields filled out. You may also need to set ``smtp_user``,
-``smtp_pass``, and ``require_transport_security``.
+headed `email`, and be sure to have at least the `smtp_host`, `smtp_port`
+and `notif_from` fields filled out.  You may also need to set `smtp_user`,
+`smtp_pass`, and `require_transport_security`.
 
-If Synapse is not configured with an SMTP server, password reset via email will
- be disabled by default.
+If email is not configured, password reset, registration and notifications via
+email will be disabled.
 
 ## Registering a user
 
diff --git a/changelog.d/6272.doc b/changelog.d/6272.doc
new file mode 100644
index 0000000000..232180bcdc
--- /dev/null
+++ b/changelog.d/6272.doc
@@ -0,0 +1 @@
+Update `INSTALL.md` Email section to talk about `account_threepid_delegates`.
\ No newline at end of file
diff --git a/docker/start.py b/docker/start.py
index e41ea20e70..6e1cb807a1 100755
--- a/docker/start.py
+++ b/docker/start.py
@@ -217,8 +217,9 @@ def main(args, environ):
         # backwards-compatibility generate-a-config-on-the-fly mode
         if "SYNAPSE_CONFIG_PATH" in environ:
             error(
-                "SYNAPSE_SERVER_NAME and SYNAPSE_CONFIG_PATH are mutually exclusive "
-                "except in `generate` or `migrate_config` mode."
+                "SYNAPSE_SERVER_NAME can only be combined with SYNAPSE_CONFIG_PATH "
+                "in `generate` or `migrate_config` mode. To start synapse using a "
+                "config file, unset the SYNAPSE_SERVER_NAME environment variable."
             )
 
         config_path = "/compiled/homeserver.yaml"