diff --git a/index.php b/index.php
index 8b79586..cfb995a 100644
--- a/index.php
+++ b/index.php
@@ -244,17 +244,17 @@
 	function inbox() {
 		global $body, $server, $username, $key_private, $directories;
 
-		//	Get the message and type
+		//	Get the message, type, and ID
 		$inbox_message = $body;
 		$inbox_type = $inbox_message["type"];
+		$inbox_id   = $inbox_message["id"];
 
-		//	If this is an Undo or Delete message, try to process it
-		if ( "Undo" == $inbox_type || "Delete" == $inbox_type ) { 
+		//	If this is an Undo, Delete, or Update message, try to process it
+		if ( "Undo" == $inbox_type || "Delete" == $inbox_type || "Update" == $inbox_type ) { 
 			undo( $inbox_message ); 
 			die();
 		}
 
-
 		//	Messages to ignore.
 		//	Some servers are very chatty. They send lots of irrelevant messages.
 		//	Before even bothering to validate them, we can delete them.
@@ -293,7 +293,7 @@
 		if ( !verifyHTTPSignature() ) { die(); }
 
 		//	If the message is valid, save the message in `/data/inbox/`
-		$uuid = uuid();
+		$uuid = uuid( $inbox_message );
 		$inbox_filename = $uuid . "." . urlencode( $inbox_type ) . ".json";
 		file_put_contents( $directories["inbox"] . "/{$inbox_filename}", json_encode( $inbox_message ) );
 
@@ -345,14 +345,30 @@
 	// Every message sent should have a unique ID. 
 	// This can be anything you like. Some servers use a random number.
 	// I prefer a date-sortable string.
-	function uuid() {
-		return sprintf( "%08x-%04x-%04x-%04x-%012x",
-			time(),
-			mt_rand(0, 0xffff),
-			mt_rand(0, 0xffff),
-			mt_rand(0, 0x3fff) | 0x8000,
-			mt_rand(0, 0xffffffffffff)
-		);
+	function uuid( $message = null) {
+		//	UUIDs that this server *sends* will be [timestamp]-[random]
+		//	65e99ab4-5d43-f074-b43e-463f9c5cf05c
+		if ( is_null( $message ) ) {
+			return sprintf( "%08x-%04x-%04x-%04x-%012x",
+				time(),
+				mt_rand(0, 0xffff),
+				mt_rand(0, 0xffff),
+				mt_rand(0, 0x3fff) | 0x8000,
+				mt_rand(0, 0xffffffffffff)
+			);
+		} else {
+			//	UUIDs that this server *saves* will be [timestamp]-[hash of message ID]
+			//	65eadace-8f434346648f6b96df89dda901c5176b10a6d83961dd3c1ac88b59b2dc327aa4
+
+			//	The message might have its own object
+			if ( isset( $message["object"]["id"] ) ) {
+				$id = $message["object"]["id"];
+			} else {
+				$id = $message["id"];
+			}
+
+			return sprintf( "%08x", time() ) . "-" . hash( "sha256", $id );
+		}
 	}
 
 	//	Headers:
@@ -1673,7 +1689,7 @@ HTML;
 	}
 
 	//	Perform the Undo action requested
-	function undo( $message) { 
+	function undo( $message ) { 
 		global $server, $directories;
 		
 		//	Validate HTTP Message Signature
@@ -1681,27 +1697,44 @@ HTML;
 
 		//	Get some basic data
 		$type = $message["type"];
+		$id   = $message["id"];
 		//	The thing being undone
 		$object      = $message["object"];
-		$object_id   = $object["id"];
-		$object_type = $object["type"];
+
+		//	Does the thing being undone have its own ID or Type?
+		if ( isset( $object["id"] ) ) {
+			$object_id   = $object["id"];
+		} else {
+			$object_id = $id;
+		}
+
+		if ( isset( $object["type"] ) ) {
+			$object_type   = $object["type"];
+		} else {
+			$object_type = $type;
+		}
+
+		//	Inbox items are stored as the hash of the original ID
+		$object_id_hash = hash( "sha256", $object_id );
 		
 		//	Find all the inbox messages which have that ID
 		$inbox_files = glob( $directories["inbox"] . "/*.json" );
 		foreach ( $inbox_files as $inbox_file ) {
-			//	Load the contents
-			$inbox_item = json_decode( file_get_contents( $inbox_file ), true );
-			//	Find the ID
-			if ( isset( $inbox_item["object"]["id"] ) ) { 
-				$inbox_id = $inbox_item["object"]["id"];
-			} else if ( isset ($inbox_item["id"] )) {
-				$inbox_id = $inbox_item["id"];
+			//	Filenames are `data/inbox/[date]-[SHA256 hash0].[Type].json
+			// Find the position of the first hyphen and the first dot
+			$hyphenPosition = strpos( $inbox_file, '-' );
+			$dotPosition    = strpos( $inbox_file, '.' );
+			
+			if ( $hyphenPosition !== false && $dotPosition !== false ) {
+				// Extract the text between the hyphen and the first dot
+				$file_id_hash = substr( $inbox_file, $hyphenPosition + 1, $dotPosition - $hyphenPosition - 1);
 			} else {
+				//	Ignore the file and move to the next.
 				continue;
 			}
 
-			//	If this has the same ID as the item being undone
-			if ( $inbox_id == $object_id ) {
+			//	If this has the same hash as the item being undone
+			if ( $object_id_hash == $file_id_hash ) {
 				//	Delete the file
 				unlink( $inbox_file );
 
@@ -1716,14 +1749,12 @@ HTML;
 			}
 		}
 		
-
 		//	If the message is valid, save the message in `/data/inbox/`
-		$uuid = uuid();
+		$uuid = uuid( $message );
 		$filename = $uuid . "." . urlencode( $type ) . ".json";
 		file_put_contents( $directories["inbox"] . "/{$filename}", json_encode( $message ) );
 	}
 
-
 //	"One to stun, two to kill, three to make sure"
 die();
 die();