diff --git a/README.md b/README.md
index 656b282..da17996 100644
--- a/README.md
+++ b/README.md
@@ -114,6 +114,7 @@ Project maintained on GitHub at [automattic/wordpress-activitypub](https://githu
 * Added: CSS class for ActivityPub comments to allow custom designs
 * Added: FEP-2677: Identifying the Application Actor
 * Added: Basic Comment Federation
+* Added: Profile Update Activities
 * Improved: WebFinger endpoints
 
 ### 1.3.0 ###
diff --git a/activitypub.php b/activitypub.php
index 55d040b..3ec6cb5 100644
--- a/activitypub.php
+++ b/activitypub.php
@@ -33,6 +33,7 @@ require_once __DIR__ . '/includes/functions.php';
 \defined( 'ACTIVITYPUB_CUSTOM_POST_CONTENT' ) || \define( 'ACTIVITYPUB_CUSTOM_POST_CONTENT', "<strong>[ap_title]</strong>\n\n[ap_content]\n\n[ap_hashtags]\n\n[ap_shortlink]" );
 \defined( 'ACTIVITYPUB_AUTHORIZED_FETCH' ) || \define( 'ACTIVITYPUB_AUTHORIZED_FETCH', false );
 \defined( 'ACTIVITYPUB_DISABLE_REWRITES' ) || \define( 'ACTIVITYPUB_DISABLE_REWRITES', false );
+\defined( 'ACTIVITYPUB_SHARED_INBOX_FEATURE' ) || \define( 'ACTIVITYPUB_SHARED_INBOX_FEATURE', false );
 
 \define( 'ACTIVITYPUB_PLUGIN_DIR', plugin_dir_path( __FILE__ ) );
 \define( 'ACTIVITYPUB_PLUGIN_BASENAME', plugin_basename( __FILE__ ) );
diff --git a/includes/class-activity-dispatcher.php b/includes/class-activity-dispatcher.php
index 7665425..6bb6a04 100644
--- a/includes/class-activity-dispatcher.php
+++ b/includes/class-activity-dispatcher.php
@@ -28,6 +28,7 @@ class Activity_Dispatcher {
 	public static function init() {
 		\add_action( 'activitypub_send_activity', array( self::class, 'send_activity' ), 10, 2 );
 		\add_action( 'activitypub_send_activity', array( self::class, 'send_activity_or_announce' ), 10, 2 );
+		\add_action( 'activitypub_send_update_profile_activity', array( self::class, 'send_profile_update' ), 10, 1 );
 	}
 
 	/**
@@ -74,19 +75,9 @@ class Activity_Dispatcher {
 			return;
 		}
 
-		$activity = $transformer->to_activity( 'Create' );
+		$activity = $transformer->to_activity( $type );
 
-		$follower_inboxes  = Followers::get_inboxes( $user_id );
-		$mentioned_inboxes = Mention::get_inboxes( $activity->get_cc() );
-
-		$inboxes = array_merge( $follower_inboxes, $mentioned_inboxes );
-		$inboxes = array_unique( $inboxes );
-
-		$json = $activity->to_json();
-
-		foreach ( $inboxes as $inbox ) {
-			safe_remote_post( $inbox, $json, $user_id );
-		}
+		self::send_activity_to_inboxes( $activity, $user_id );
 	}
 
 	/**
@@ -112,12 +103,60 @@ class Activity_Dispatcher {
 		$user_id  = $transformer->get_wp_user_id();
 		$activity = $transformer->to_activity( 'Announce' );
 
-		$follower_inboxes  = Followers::get_inboxes( $user_id );
-		$mentioned_inboxes = Mention::get_inboxes( $activity->get_cc() );
+		self::send_activity_to_inboxes( $activity, $user_id );
+	}
+
+	/**
+	 * Send a "Update" Activity when a user updates their profile.
+	 *
+	 * @param int $user_id The user ID to send an update for.
+	 *
+	 * @return void
+	 */
+	public static function send_profile_update( $user_id ) {
+		$user = Users::get_by_various( $user_id );
+
+		// bail if that's not a good user
+		if ( is_wp_error( $user ) ) {
+			return;
+		}
+
+		// build the update
+		$activity = new Activity();
+		$activity->set_id( $user->get_url() . '#update' );
+		$activity->set_type( 'Update' );
+		$activity->set_actor( $user->get_url() );
+		$activity->set_object( $user->get_url() );
+		$activity->set_to( 'https://www.w3.org/ns/activitystreams#Public' );
+
+		// send the update
+		self::send_activity_to_inboxes( $activity, $user_id );
+	}
+
+	/**
+	 * Send an Activity to all followers and mentioned users.
+	 *
+	 * @param Activity $activity The ActivityPub Activity.
+	 * @param int      $user_id  The user ID.
+	 *
+	 * @return void
+	 */
+	private static function send_activity_to_inboxes( $activity, $user_id ) {
+		$follower_inboxes = Followers::get_inboxes( $user_id );
+
+		$mentioned_inboxes = array();
+		$cc = $activity->get_cc();
+		if ( $cc ) {
+			$mentioned_inboxes = Mention::get_inboxes( $cc );
+		}
 
 		$inboxes = array_merge( $follower_inboxes, $mentioned_inboxes );
 		$inboxes = array_unique( $inboxes );
 
+		if ( empty( $inboxes ) ) {
+			return;
+		}
+
 		$json = $activity->to_json();
 
 		foreach ( $inboxes as $inbox ) {
diff --git a/includes/class-admin.php b/includes/class-admin.php
index 7acfff9..dca3aee 100644
--- a/includes/class-admin.php
+++ b/includes/class-admin.php
@@ -18,6 +18,7 @@ class Admin {
 		\add_action( 'admin_init', array( self::class, 'register_settings' ) );
 		\add_action( 'personal_options_update', array( self::class, 'save_user_description' ) );
 		\add_action( 'admin_enqueue_scripts', array( self::class, 'enqueue_scripts' ) );
+		\add_action( 'admin_notices', array( self::class, 'admin_notices' ) );
 
 		if ( ! is_user_disabled( get_current_user_id() ) ) {
 			\add_action( 'show_user_profile', array( self::class, 'add_profile' ) );
@@ -46,6 +47,37 @@ class Admin {
 		}
 	}
 
+	/**
+	 * Display admin menu notices about configuration problems or conflicts.
+	 *
+	 * @return void
+	 */
+	public static function admin_notices() {
+		$permalink_structure = \get_option( 'permalink_structure' );
+		if ( empty( $permalink_structure ) ) {
+			$admin_notice = \__( 'You are using the ActivityPub plugin without setting a permalink structure. This will prevent ActivityPub from working.  Please set a permalink structure.', 'activitypub' );
+			self::show_admin_notice( $admin_notice, 'error' );
+		}
+	}
+
+	/**
+	 * Display one admin menu notice about configuration problems or conflicts.
+	 *
+	 * @param string $admin_notice The notice to display.
+	 * @param string $level The level of the notice (error, warning, success, info).
+	 *
+	 * @return void
+	 */
+	private static function show_admin_notice( $admin_notice, $level ) {
+		?>
+
+		<div class="notice notice-<?php echo esc_attr( $level ); ?>">
+			<p><?php echo wp_kses( $admin_notice, 'data' ); ?></p>
+		</div>
+
+		<?php
+	}
+
 	/**
 	 * Load settings page
 	 */
diff --git a/includes/class-scheduler.php b/includes/class-scheduler.php
index 61deab7..60e3f00 100644
--- a/includes/class-scheduler.php
+++ b/includes/class-scheduler.php
@@ -6,12 +6,15 @@ use Activitypub\Collection\Users;
 use Activitypub\Collection\Followers;
 use Activitypub\Transformer\Post;
 
+use function Activitypub\is_user_type_disabled;
+
 /**
  * ActivityPub Scheduler Class
  *
  * @author Matthias Pfefferle
  */
 class Scheduler {
+
 	/**
 	 * Initialize the class, registering WordPress hooks
 	 */
@@ -58,6 +61,22 @@ class Scheduler {
 
 		// Migration
 		\add_action( 'admin_init', array( self::class, 'schedule_migration' ) );
+
+		// profile updates for blog options
+		if ( ! is_user_type_disabled( 'blog' ) ) {
+			\add_action( 'update_option_site_icon', array( self::class, 'blog_user_update' ) );
+			\add_action( 'update_option_blogdescription', array( self::class, 'blog_user_update' ) );
+			\add_action( 'update_option_blogname', array( self::class, 'blog_user_update' ) );
+			\add_filter( 'pre_set_theme_mod_custom_logo', array( self::class, 'blog_user_update' ) );
+			\add_filter( 'pre_set_theme_mod_header_image', array( self::class, 'blog_user_update' ) );
+		}
+
+		// profile updates for user options
+		if ( ! is_user_type_disabled( 'user' ) ) {
+			\add_action( 'wp_update_user', array( self::class, 'user_update' ) );
+			\add_action( 'updated_user_meta', array( self::class, 'user_meta_update' ), 10, 3 );
+			// @todo figure out a feasible way of updating the header image since it's not unique to any user.
+		}
 	}
 
 	/**
@@ -255,4 +274,68 @@ class Scheduler {
 			\wp_schedule_single_event( \time(), 'activitypub_schedule_migration' );
 		}
 	}
+
+	/**
+	 * Send a profile update when relevant user meta is updated.
+	 *
+	 * @param  int    $meta_id Meta ID being updated.
+	 * @param  int    $user_id User ID being updated.
+	 * @param  string $meta_key Meta key being updated.
+	 *
+	 * @return void
+	 */
+	public static function user_meta_update( $meta_id, $user_id, $meta_key ) {
+		// don't bother if the user can't publish
+		if ( ! \user_can( $user_id, 'publish_posts' ) ) {
+			return;
+		}
+		// the user meta fields that affect a profile.
+		$fields = array(
+			'activitypub_user_description',
+			'description',
+			'user_url',
+			'display_name',
+		);
+		if ( in_array( $meta_key, $fields, true ) ) {
+			self::schedule_profile_update( $user_id );
+		}
+	}
+
+	/**
+	 * Send a profile update when a user is updated.
+	 *
+	 * @param  int $user_id User ID being updated.
+	 *
+	 * @return void
+	 */
+	public static function user_update( $user_id ) {
+		// don't bother if the user can't publish
+		if ( ! \user_can( $user_id, 'publish_posts' ) ) {
+			return;
+		}
+
+		self::schedule_profile_update( $user_id );
+	}
+
+	/**
+	 * Theme mods only have a dynamic filter so we fudge it like this.
+	 * @param  mixed $value
+	 * @return mixed
+	 */
+	public static function blog_user_update( $value = null ) {
+		self::schedule_profile_update( 0 );
+		return $value;
+	}
+
+	/**
+	 * Send a profile update to all followers. Gets hooked into all relevant options/meta etc.
+	 * @param int $user_id  The user ID to update (Could be 0 for Blog-User).
+	 */
+	public static function schedule_profile_update( $user_id ) {
+		\wp_schedule_single_event(
+			\time(),
+			'activitypub_send_update_profile_activity',
+			array( $user_id )
+		);
+	}
 }
diff --git a/includes/handler/class-create.php b/includes/handler/class-create.php
index 2e5d76a..64788da 100644
--- a/includes/handler/class-create.php
+++ b/includes/handler/class-create.php
@@ -15,7 +15,12 @@ class Create {
 	 * Initialize the class, registering WordPress hooks
 	 */
 	public static function init() {
-		\add_action( 'activitypub_inbox_create', array( self::class, 'handle_create' ), 10, 3 );
+		\add_action(
+			'activitypub_inbox_create',
+			array( self::class, 'handle_create' ),
+			10,
+			3
+		);
 	}
 
 	/**
diff --git a/includes/handler/class-delete.php b/includes/handler/class-delete.php
index a8611d4..f2571c0 100644
--- a/includes/handler/class-delete.php
+++ b/includes/handler/class-delete.php
@@ -15,11 +15,24 @@ class Delete {
 	 * Initialize the class, registering WordPress hooks
 	 */
 	public static function init() {
-		\add_action( 'activitypub_inbox_delete', array( self::class, 'handle_delete' ), 10, 2 );
+		\add_action(
+			'activitypub_inbox_delete',
+			array( self::class, 'handle_delete' )
+		);
+
 		// defer signature verification for `Delete` requests.
-		\add_filter( 'activitypub_defer_signature_verification', array( self::class, 'defer_signature_verification' ), 10, 2 );
+		\add_filter(
+			'activitypub_defer_signature_verification',
+			array( self::class, 'defer_signature_verification' ),
+			10,
+			2
+		);
+
 		// side effect
-		\add_action( 'activitypub_delete_actor_interactions', array( self::class, 'delete_interactions' ), 10, 1 );
+		\add_action(
+			'activitypub_delete_actor_interactions',
+			array( self::class, 'delete_interactions' )
+		);
 	}
 
 	/**
@@ -28,7 +41,7 @@ class Delete {
 	 * @param array $activity The delete activity.
 	 * @param int   $user_id  The ID of the user performing the delete activity.
 	 */
-	public static function handle_delete( $activity, $user_id ) {
+	public static function handle_delete( $activity ) {
 		$object_type = isset( $activity['object']['type'] ) ? $activity['object']['type'] : '';
 
 		switch ( $object_type ) {
@@ -39,7 +52,7 @@ class Delete {
 			case 'Organization':
 			case 'Service':
 			case 'Application':
-				self::maybe_delete_follower( $user_id, $activity );
+				self::maybe_delete_follower( $activity );
 				break;
 			// Object and Link Types
 			// @see https://www.w3.org/TR/activitystreams-vocabulary/#object-types
diff --git a/includes/handler/class-follow.php b/includes/handler/class-follow.php
index 6855dbd..810680b 100644
--- a/includes/handler/class-follow.php
+++ b/includes/handler/class-follow.php
@@ -14,8 +14,17 @@ class Follow {
 	 * Initialize the class, registering WordPress hooks
 	 */
 	public static function init() {
-		\add_action( 'activitypub_inbox_follow', array( self::class, 'handle_follow' ), 10, 2 );
-		\add_action( 'activitypub_followers_post_follow', array( self::class, 'send_follow_response' ), 10, 4 );
+		\add_action(
+			'activitypub_inbox_follow',
+			array( self::class, 'handle_follow' )
+		);
+
+		\add_action(
+			'activitypub_followers_post_follow',
+			array( self::class, 'send_follow_response' ),
+			10,
+			4
+		);
 	}
 
 	/**
@@ -24,11 +33,30 @@ class Follow {
 	 * @param array $activity The activity object
 	 * @param int   $user_id  The user ID
 	 */
-	public static function handle_follow( $activity, $user_id ) {
-		// save follower
-		$follower = Followers::add_follower( $user_id, $activity['actor'] );
+	public static function handle_follow( $activity ) {
+		$user = Users::get_by_resource( $activity['object'] );
 
-		do_action( 'activitypub_followers_post_follow', $activity['actor'], $activity, $user_id, $follower );
+		if ( ! $user || is_wp_error( $user ) ) {
+			// If we can not find a user,
+			// we can not initiate a follow process
+			return;
+		}
+
+		$user_id = $user->get__id();
+
+		// save follower
+		$follower = Followers::add_follower(
+			$user_id,
+			$activity['actor']
+		);
+
+		do_action(
+			'activitypub_followers_post_follow',
+			$activity['actor'],
+			$activity,
+			$user_id,
+			$follower
+		);
 	}
 
 	/**
diff --git a/includes/handler/class-undo.php b/includes/handler/class-undo.php
index 13c06f3..74d3dca 100644
--- a/includes/handler/class-undo.php
+++ b/includes/handler/class-undo.php
@@ -1,6 +1,7 @@
 <?php
 namespace Activitypub\Handler;
 
+use Activitypub\Collection\Users;
 use Activitypub\Collection\Followers;
 
 /**
@@ -11,7 +12,10 @@ class Undo {
 	 * Initialize the class, registering WordPress hooks
 	 */
 	public static function init() {
-		\add_action( 'activitypub_inbox_undo', array( self::class, 'handle_undo' ), 10, 2 );
+		\add_action(
+			'activitypub_inbox_undo',
+			array( self::class, 'handle_undo' )
+		);
 	}
 
 	/**
@@ -20,11 +24,23 @@ class Undo {
 	 * @param array $activity The JSON "Undo" Activity
 	 * @param int   $user_id  The ID of the ID of the WordPress User
 	 */
-	public static function handle_undo( $activity, $user_id ) {
+	public static function handle_undo( $activity ) {
 		if (
 			isset( $activity['object']['type'] ) &&
-			'Follow' === $activity['object']['type']
+			'Follow' === $activity['object']['type'] &&
+			isset( $activity['object']['object'] ) &&
+			filter_var( $activity['object']['object'], FILTER_VALIDATE_URL )
 		) {
+			$user = Users::get_by_resource( $activity['object']['object'] );
+
+			if ( ! $user || is_wp_error( $user ) ) {
+				// If we can not find a user,
+				// we can not initiate a follow process
+				return;
+			}
+
+			$user_id = $user->get__id();
+
 			Followers::remove_follower( $user_id, $activity['actor'] );
 		}
 	}
diff --git a/includes/handler/class-update.php b/includes/handler/class-update.php
index 00e0430..002c3d5 100644
--- a/includes/handler/class-update.php
+++ b/includes/handler/class-update.php
@@ -14,7 +14,10 @@ class Update {
 	 * Initialize the class, registering WordPress hooks
 	 */
 	public static function init() {
-		\add_action( 'activitypub_inbox_update', array( self::class, 'handle_update' ), 10, 2 );
+		\add_action(
+			'activitypub_inbox_update',
+			array( self::class, 'handle_update' )
+		);
 	}
 
 	/**
@@ -23,7 +26,7 @@ class Update {
 	 * @param array                $array   The activity-object
 	 * @param int                  $user_id The id of the local blog-user
 	 */
-	public static function handle_update( $array, $user_id ) {
+	public static function handle_update( $array ) {
 		$object_type = isset( $array['object']['type'] ) ? $array['object']['type'] : '';
 
 		switch ( $object_type ) {
@@ -45,7 +48,7 @@ class Update {
 			case 'Video':
 			case 'Event':
 			case 'Document':
-				self::update_interaction( $array, $user_id );
+				self::update_interaction( $array );
 				break;
 			// Minimal Activity
 			// @see https://www.w3.org/TR/activitystreams-core/#example-1
@@ -62,7 +65,7 @@ class Update {
 	 *
 	 * @return void
 	 */
-	public static function update_interaction( $activity, $user_id ) {
+	public static function update_interaction( $activity ) {
 		$state    = Interactions::update_comment( $activity );
 		$reaction = null;
 
@@ -70,7 +73,7 @@ class Update {
 			$reaction = \get_comment( $state );
 		}
 
-		\do_action( 'activitypub_handled_update', $activity, $user_id, $state, $reaction );
+		\do_action( 'activitypub_handled_update', $activity, null, $state, $reaction );
 	}
 
 	/**
diff --git a/includes/model/class-user.php b/includes/model/class-user.php
index c713434..c22f83c 100644
--- a/includes/model/class-user.php
+++ b/includes/model/class-user.php
@@ -226,6 +226,18 @@ class User extends Actor {
 		return get_rest_url_by_path( sprintf( 'users/%d/collections/featured', $this->get__id() ) );
 	}
 
+	public function get_endpoints() {
+		$endpoints = null;
+
+		if ( ACTIVITYPUB_SHARED_INBOX_FEATURE ) {
+			$endpoints = array(
+				'sharedInbox' => get_rest_url_by_path( 'inbox' ),
+			);
+		}
+
+		return $endpoints;
+	}
+
 	/**
 	 * Extend the User-Output with Attachments.
 	 *
diff --git a/includes/rest/class-inbox.php b/includes/rest/class-inbox.php
index 938ca90..c527040 100644
--- a/includes/rest/class-inbox.php
+++ b/includes/rest/class-inbox.php
@@ -94,11 +94,8 @@ class Inbox {
 		$json->generator = 'http://wordpress.org/?v=' . \get_bloginfo_rss( 'version' );
 		$json->type = 'OrderedCollectionPage';
 		$json->partOf = get_rest_url_by_path( sprintf( 'users/%d/inbox', $user->get__id() ) ); // phpcs:ignore
-
 		$json->totalItems = 0; // phpcs:ignore
-
 		$json->orderedItems = array(); // phpcs:ignore
-
 		$json->first = $json->partOf; // phpcs:ignore
 
 		// filter output
@@ -155,37 +152,10 @@ class Inbox {
 		$data     = $request->get_json_params();
 		$activity = Activity::init_from_array( $data );
 		$type     = $request->get_param( 'type' );
-		$users    = self::get_recipients( $data );
+		$type     = \strtolower( $type );
 
-		if ( ! $users ) {
-			return new WP_Error(
-				'rest_invalid_param',
-				\__( 'No recipients found', 'activitypub' ),
-				array(
-					'status' => 400,
-					'params' => array(
-						'to' => \__( 'Please check/validate "to" field', 'activitypub' ),
-						'bto' => \__( 'Please check/validate "bto" field', 'activitypub' ),
-						'cc' => \__( 'Please check/validate "cc" field', 'activitypub' ),
-						'bcc' => \__( 'Please check/validate "bcc" field', 'activitypub' ),
-						'audience' => \__( 'Please check/validate "audience" field', 'activitypub' ),
-					),
-				)
-			);
-		}
-
-		foreach ( $users as $user ) {
-			$user = User_Collection::get_by_various( $user );
-
-			if ( is_wp_error( $user ) ) {
-				continue;
-			}
-
-			$type = \strtolower( $type );
-
-			\do_action( 'activitypub_inbox', $data, $user->ID, $type, $activity );
-			\do_action( "activitypub_inbox_{$type}", $data, $user->ID, $activity );
-		}
+		\do_action( 'activitypub_inbox', $data, null, $type, $activity );
+		\do_action( "activitypub_inbox_{$type}", $data, null, $activity );
 
 		$rest_response = new WP_REST_Response( array(), 202 );
 		$rest_response->header( 'Content-Type', 'application/activity+json; charset=' . get_option( 'blog_charset' ) );
diff --git a/includes/transformer/class-post.php b/includes/transformer/class-post.php
index b5cdd8d..b5eba90 100644
--- a/includes/transformer/class-post.php
+++ b/includes/transformer/class-post.php
@@ -395,7 +395,7 @@ class Post extends Base {
 	 *
 	 * @return string The Object-Type.
 	 */
-	protected function get_object_type() {
+	protected function get_type() {
 		if ( 'wordpress-post-format' !== \get_option( 'activitypub_object_type', 'note' ) ) {
 			return \ucfirst( \get_option( 'activitypub_object_type', 'note' ) );
 		}
diff --git a/readme.txt b/readme.txt
index 510a3ca..f31f3ab 100644
--- a/readme.txt
+++ b/readme.txt
@@ -114,6 +114,7 @@ Project maintained on GitHub at [automattic/wordpress-activitypub](https://githu
 * Added: CSS class for ActivityPub comments to allow custom designs
 * Added: FEP-2677: Identifying the Application Actor
 * Added: Basic Comment Federation
+* Added: Profile Update Activities
 * Improved: WebFinger endpoints
 
 = 1.3.0 =
diff --git a/tests/test-class-admin.php b/tests/test-class-admin.php
new file mode 100644
index 0000000..73db3be
--- /dev/null
+++ b/tests/test-class-admin.php
@@ -0,0 +1,18 @@
+<?php
+class Test_Admin extends WP_UnitTestCase {
+	public function test_no_permalink_structure_has_errors() {
+		\add_option( 'permalink_structure', '' );
+		\do_action( 'admin_notices' );
+		$this->expectOutputRegex( "/notice-error/" );
+
+		\delete_option( 'permalink_structure' );
+	}
+
+	public function test_has_permalink_structure_no_errors() {
+		\add_option( 'permalink_structure', '/archives/%post_id%' );
+		\do_action( 'admin_notices' );
+		$this->expectOutputRegex( "/^((?!notice-error).)*$/s" );
+
+		\delete_option( 'permalink_structure' );
+	}
+}