diff --git a/src/client/components/components-web-view.vala b/src/client/components/components-web-view.vala
index 2b373170..c746c441 100644
--- a/src/client/components/components-web-view.vala
+++ b/src/client/components/components-web-view.vala
@@ -198,6 +198,24 @@ public abstract class Components.WebView : WebKit.WebView, Geary.BaseInterface {
     /** Delegate for UserContentManager message callbacks. */
     public delegate void JavaScriptMessageHandler(WebKit.JavascriptResult js_result);
 
+    /**
+     * Delegate for message handler callbacks.
+     *
+     * @see register_message_callback
+     */
+    protected delegate void MessageCallback(GLib.Variant? parameters);
+
+    // Work around for not being able to put delegates in a Gee collection.
+    private class MessageCallable {
+
+        public unowned MessageCallback handler;
+
+        public MessageCallable(MessageCallback handler) {
+            this.handler = handler;
+        }
+
+    }
+
     /**
      * Determines if the view's content has been fully loaded.
      *
@@ -263,6 +281,8 @@ public abstract class Components.WebView : WebKit.WebView, Geary.BaseInterface {
 
     private Gee.List<ulong> registered_message_handlers =
         new Gee.LinkedList<ulong>();
+    private Gee.Map<string,MessageCallable> message_handlers =
+        new Gee.HashMap<string,MessageCallable>();
 
     private double webkit_reported_height = 0;
 
@@ -359,6 +379,7 @@ public abstract class Components.WebView : WebKit.WebView, Geary.BaseInterface {
             this.user_content_manager.disconnect(id);
         }
         this.registered_message_handlers.clear();
+        this.message_handlers.clear();
         base.destroy();
     }
 
@@ -568,6 +589,14 @@ public abstract class Components.WebView : WebKit.WebView, Geary.BaseInterface {
         }
     }
 
+    /**
+     * Registers a callback for a specific WebKit user message.
+     */
+    protected void register_message_callback(string name,
+                                             MessageCallback handler) {
+        this.message_handlers.set(name, new MessageCallable(handler));
+    }
+
     private void init(Application.Configuration config) {
         // XXX get the allow prefix from the extension somehow
 
@@ -595,6 +624,8 @@ public abstract class Components.WebView : WebKit.WebView, Geary.BaseInterface {
             SELECTION_CHANGED, on_selection_changed
         );
 
+        this.user_message_received.connect(this.on_message_received);
+
         // Manage zoom level, ensure it's sane
         config.bind(Application.Configuration.CONVERSATION_VIEWER_ZOOM_KEY, this, "zoom_level");
         if (this.zoom_level < ZOOM_MIN) {
@@ -803,6 +834,30 @@ public abstract class Components.WebView : WebKit.WebView, Geary.BaseInterface {
         }
     }
 
+    private bool on_message_received(WebKit.UserMessage message) {
+        if (message.name == MESSAGE_EXCEPTION_NAME) {
+            var detail = new GLib.VariantDict(message.parameters);
+            var name = detail.lookup_value("name", GLib.VariantType.STRING) as string;
+            var log_message = detail.lookup_value("message", GLib.VariantType.STRING) as string;
+            warning(
+                "Error sending message from JS: %s: %s",
+                name ?? "unknown",
+                log_message ?? "unknown"
+            );
+        } else if (this.message_handlers.has_key(message.name)) {
+            debug(
+                "Message received: %s(%s)",
+                message.name,
+                message.parameters != null ? message.parameters.print(true) : ""
+            );
+            MessageCallable callback = this.message_handlers.get(message.name);
+            callback.handler(message.parameters);
+        } else {
+            warning("Message with unknown handler received: %s", message.name);
+        }
+        return true;
+    }
+
 }
 
 // XXX this needs to be moved into the libsoup bindings
diff --git a/src/client/web-process/web-process-extension.vala b/src/client/web-process/web-process-extension.vala
index 89d9a1e3..31f2b0f0 100644
--- a/src/client/web-process/web-process-extension.vala
+++ b/src/client/web-process/web-process-extension.vala
@@ -38,6 +38,8 @@ public class GearyWebExtension : Object {
 
     private const string[] ALLOWED_SCHEMES = { "cid", "geary", "data", "blob" };
 
+    private const string EXTENSION_CLASS_VAR = "_GearyWebExtension";
+    private const string EXTENSION_CLASS_SEND = "send";
     private const string REMOTE_LOAD_VAR = "_gearyAllowRemoteResourceLoads";
 
     private WebKit.WebExtension extension;
@@ -180,6 +182,25 @@ public class GearyWebExtension : Object {
                                  WebKit.WebPage page) {
         WebKit.Frame frame = page.get_main_frame();
         JSC.Context context = frame.get_js_context();
+
+        var extension_class = context.register_class(
+            this.get_type().name(),
+            null,
+            null,
+            null
+        );
+        extension_class.add_method(
+            EXTENSION_CLASS_SEND,
+            (instance, values) => {
+                return this.on_page_send_message(page, values);
+            },
+            GLib.Type.NONE
+        );
+        context.set_value(
+            EXTENSION_CLASS_VAR,
+            new JSC.Value.object(context, extension_class, extension_class)
+        );
+
         context.set_value(
             REMOTE_LOAD_VAR,
             new JSC.Value.boolean(context, false)
@@ -259,4 +280,46 @@ public class GearyWebExtension : Object {
         return true;
     }
 
+    private bool on_page_send_message(WebKit.WebPage page,
+                                      GLib.GenericArray<JSC.Value> args) {
+        WebKit.UserMessage? message = null;
+        if (args.length > 0) {
+            var name = args.get(0).to_string();
+            GLib.Variant? parameters = null;
+            if (args.length > 1) {
+                JSC.Value param_value = args.get(1);
+                try {
+                    int len = Util.JS.to_int32(
+                        param_value.object_get_property("length")
+                    );
+                    if (len == 1) {
+                        parameters = Util.JS.value_to_variant(
+                            param_value.object_get_property_at_index(0)
+                        );
+                    } else if (len > 1) {
+                        parameters = Util.JS.value_to_variant(param_value);
+                    }
+                } catch (Util.JS.Error err) {
+                    message = to_exception_message(
+                        this.get_type().name(), err.message
+                    );
+                }
+            }
+            if (message == null) {
+                message = new WebKit.UserMessage(name, parameters);
+            }
+        }
+        if (message == null) {
+            var log_message = "Not enough parameters for JS call to %s.%s()".printf(
+                EXTENSION_CLASS_VAR,
+                EXTENSION_CLASS_SEND
+            );
+            debug(log_message);
+            message = to_exception_message(this.get_type().name(), log_message);
+        }
+
+        page.send_message_to_view.begin(message, null);
+        return true;
+    }
+
 }
diff --git a/ui/components-web-view.js b/ui/components-web-view.js
index 0f932a19..35e82dfc 100644
--- a/ui/components-web-view.js
+++ b/ui/components-web-view.js
@@ -200,3 +200,12 @@ PageState.prototype = {
         throw this.testResult;
     }
 };
+
+let MessageSender = function(name) {
+    return function() {
+        // Since typeof(arguments) == 'object', convert to an array so
+        // that Components.WebView.MessageCallback callbacks get
+        // arrays or tuples rather than dicts as arguments
+        _GearyWebExtension.send(name, Array.from(arguments));
+    };
+};