diff --git a/core/src/main/java/google/registry/batch/BatchModule.java b/core/src/main/java/google/registry/batch/BatchModule.java
index b2854c2fa..047377752 100644
--- a/core/src/main/java/google/registry/batch/BatchModule.java
+++ b/core/src/main/java/google/registry/batch/BatchModule.java
@@ -54,9 +54,9 @@ public class BatchModule {
   static final int DEFAULT_MAX_QPS = 10;
 
   @Provides
-  @Parameter("sender")
-  static String provideSender(HttpServletRequest req) {
-    return extractRequiredParameter(req, "sender");
+  @Parameter("replyTo")
+  static String provideReplyTo(HttpServletRequest req) {
+    return extractRequiredParameter(req, "replyTo");
   }
 
   @Provides
diff --git a/core/src/main/java/google/registry/batch/CannedScriptExecutionAction.java b/core/src/main/java/google/registry/batch/CannedScriptExecutionAction.java
index a83e48997..7ea738723 100644
--- a/core/src/main/java/google/registry/batch/CannedScriptExecutionAction.java
+++ b/core/src/main/java/google/registry/batch/CannedScriptExecutionAction.java
@@ -18,7 +18,9 @@ import static google.registry.request.Action.Method.GET;
 import static google.registry.request.Action.Method.POST;
 
 import com.google.api.services.gmail.Gmail;
+import com.google.common.collect.ImmutableList;
 import com.google.common.flogger.FluentLogger;
+import com.google.common.net.MediaType;
 import dagger.Lazy;
 import google.registry.config.RegistryConfig.Config;
 import google.registry.groups.GmailClient;
@@ -31,6 +33,7 @@ import google.registry.util.Retrier;
 import jakarta.inject.Inject;
 import jakarta.mail.internet.AddressException;
 import jakarta.mail.internet.InternetAddress;
+import java.util.Optional;
 
 /**
  * Action that executes a canned script specified by the caller.
@@ -62,13 +65,16 @@ public class CannedScriptExecutionAction implements Runnable {
   @Inject Response response;
 
   @Inject
-  @Parameter("sender")
-  String sender;
+  @Parameter("replyTo")
+  String replyTo;
 
   @Inject
   @Parameter("receiver")
   String receiver;
 
+  @Config("invoiceReplyToEmailAddress")
+  Optional<InternetAddress> replyToEmailAddressFromConfig;
+
   @Inject
   CannedScriptExecutionAction() {}
 
@@ -77,20 +83,36 @@ public class CannedScriptExecutionAction implements Runnable {
     // For b/510340944, validating a new G Workspace user can send email. Code below can be
     // removed or changed afterward.
     try {
-      logger.atInfo().log("Sending email from %s to %s", sender, receiver);
+      logger.atInfo().log("Sending email to %s with replyTo %s", receiver, replyTo);
       GmailClient gmailClient =
-          new GmailClient(
-              gmail, retrier, isEmailSendingEnabled, sender, sender, new InternetAddress(sender));
+          new GmailClient(gmail, retrier, isEmailSendingEnabled, new InternetAddress(replyTo));
       gmailClient.sendEmail(
           EmailMessage.newBuilder()
               .addRecipient(new InternetAddress(receiver))
-              .setSubject(String.format("Email send test from %s", sender))
-              .setBody(String.format("This is a test email sent from %s to %s.", sender, receiver))
+              .setSubject(String.format("Email with manually set replyTo header %s", replyTo))
+              .setBody("See subject")
               .build());
-      response.setPayload("Email sent successfully.");
+
+      try {
+        Thread.sleep(1000);
+      } catch (InterruptedException e) {
+        Thread.currentThread().interrupt();
+      }
+
+      gmailClient.sendEmail(
+          EmailMessage.newBuilder()
+              .setSubject(
+                  String.format(
+                      "Email with injected replyTo header %s", replyToEmailAddressFromConfig))
+              .setBody("See header")
+              .setRecipients(ImmutableList.of(new InternetAddress(receiver)))
+              .setReplyToEmailAddress(replyToEmailAddressFromConfig)
+              .setContentType(MediaType.HTML_UTF_8)
+              .build());
+      response.setPayload("Emails sent successfully.");
     } catch (AddressException e) {
       logger.atWarning().withCause(e).log(
-          "Invalid email address: sender=%s, receiver=%s", sender, receiver);
+          "Invalid email address: sender=%s, receiver=%s", replyTo, receiver);
       response.setStatus(400);
       response.setPayload("Invalid email address provided.");
     } catch (Exception e) {
diff --git a/core/src/main/java/google/registry/groups/GmailClient.java b/core/src/main/java/google/registry/groups/GmailClient.java
index 32245b0f0..d66ec18c7 100644
--- a/core/src/main/java/google/registry/groups/GmailClient.java
+++ b/core/src/main/java/google/registry/groups/GmailClient.java
@@ -56,9 +56,9 @@ public final class GmailClient {
   private final InternetAddress outgoingEmailAddressWithUsername;
   private final InternetAddress replyToEmailAddress;
 
-  // TODO(b/510340944): make package private after feature is rolled out
+  // TODO(b/510340944): drop sender info. Sender is determined by the Gmail credential owner.
   @Inject
-  public GmailClient(
+  GmailClient(
       Lazy<Gmail> gmail,
       Retrier retrier,
       @Config("isEmailSendingEnabled") boolean isEmailSendingEnabled,
@@ -78,6 +78,20 @@ public final class GmailClient {
     }
   }
 
+  // TODO(b/510340944): Remove this experiment method
+  public GmailClient(
+      Lazy<Gmail> gmail,
+      Retrier retrier,
+      @Config("isEmailSendingEnabled") boolean isEmailSendingEnabled,
+      @Config("replyToEmailAddress") InternetAddress replyToEmailAddress) {
+
+    this.gmail = gmail;
+    this.retrier = retrier;
+    this.isEmailSendingEnabled = isEmailSendingEnabled;
+    this.replyToEmailAddress = replyToEmailAddress;
+    this.outgoingEmailAddressWithUsername = null;
+  }
+
   /**
    * Sends {@code emailMessage} using {@link Gmail}.
    */
@@ -117,7 +131,9 @@ public final class GmailClient {
     try {
       MimeMessage msg =
           new MimeMessage(Session.getDefaultInstance(new Properties(), /* authenticator= */ null));
-      msg.setFrom(this.outgoingEmailAddressWithUsername);
+      if (this.outgoingEmailAddressWithUsername != null) {
+        msg.setFrom(this.outgoingEmailAddressWithUsername);
+      }
       msg.setReplyTo(
           new InternetAddress[] {emailMessage.replyToEmailAddress().orElse(replyToEmailAddress)});
       msg.addRecipients(