diff --git a/api/src/org/labkey/api/util/SmtpTransportProvider.java b/api/src/org/labkey/api/util/SmtpTransportProvider.java
index 5825b583aa4..654af1599d9 100644
--- a/api/src/org/labkey/api/util/SmtpTransportProvider.java
+++ b/api/src/org/labkey/api/util/SmtpTransportProvider.java
@@ -56,7 +56,7 @@ public String getPropertyName()
         @Override
         public String getDescription()
         {
-            return "One property for each JavaMail SMTP setting, documented here: https://javaee.github.io/javamail/docs/api/com/sun/mail/smtp/package-summary.html";
+            return "No longer supported. Configure SMTP settings in application.properties.";
         }
     }
 
@@ -69,31 +69,30 @@ public String getName()
     @Override
     public void loadConfiguration()
     {
-        try
-        {
-            // Load from startup properties group "mail_smtp"
-            ModuleLoader.getInstance().handleStartupProperties(
-                new LenientStartupPropertyHandler<>("mail_smtp", new SmtpStartupProperty())
+        // TODO: Startup failure if SMTP startup properties are present, for now. Remove in 26.11.
+        ModuleLoader.getInstance().handleStartupProperties(
+            new LenientStartupPropertyHandler<>("mail_smtp", new SmtpStartupProperty())
+            {
+                @Override
+                public void handle(Collection<StartupPropertyEntry> entries)
                 {
-                    @Override
-                    public void handle(Collection<StartupPropertyEntry> entries)
+                    if (!entries.isEmpty())
                     {
-                        entries.forEach(entry ->
-                            _properties.put("mail.smtp." + entry.getName(), entry.getValue()));
+                        throw new ConfigurationException("Configuring SMTP via startup properties is no longer supported. Use application.properties.");
                     }
-                });
+                }
+            });
 
-            // Fallback: check ServletContext for SMTP settings
-            if (_properties.isEmpty())
+        try
+        {
+            // Load SMTP settings from ServletContext (populated from application.properties)
+            ServletContext context = ModuleLoader.getServletContext();
+            Enumeration<String> names = Objects.requireNonNull(context).getInitParameterNames();
+            while (names.hasMoreElements())
             {
-                ServletContext context = ModuleLoader.getServletContext();
-                Enumeration<String> names = Objects.requireNonNull(context).getInitParameterNames();
-                while (names.hasMoreElements())
-                {
-                    String name = names.nextElement();
-                    if (name.startsWith("mail.smtp."))
-                        _properties.put(name, context.getInitParameter(name));
-                }
+                String name = names.nextElement();
+                if (name.startsWith("mail.smtp."))
+                    _properties.put(name, context.getInitParameter(name));
             }
 
             // Create session if configured