diff --git a/server/message_cache.go b/server/message_cache.go
index 4a48ac1a..8e787db3 100644
--- a/server/message_cache.go
+++ b/server/message_cache.go
@@ -23,6 +23,7 @@ const (
 			id INTEGER PRIMARY KEY AUTOINCREMENT,
 			mid TEXT NOT NULL,
 			time INT NOT NULL,
+			updated INT NOT NULL,
 			topic TEXT NOT NULL,
 			message TEXT NOT NULL,
 			title TEXT NOT NULL,
@@ -43,41 +44,47 @@ const (
 		COMMIT;
 	`
 	insertMessageQuery = `
-		INSERT INTO messages (mid, time, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding, published) 
-		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+		INSERT INTO messages (mid, time, updated, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding, published) 
+		VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
 	`
+	updateMessageQuery           = `UPDATE messages SET updated = ?, message = ?, title = ?, priority = ?, tags = ?, click = ? WHERE topic = ? AND mid = ?`
 	pruneMessagesQuery           = `DELETE FROM messages WHERE time < ? AND published = 1`
 	selectRowIDFromMessageID     = `SELECT id FROM messages WHERE topic = ? AND mid = ?`
 	selectMessagesSinceTimeQuery = `
-		SELECT mid, time, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding
+		SELECT mid, time, updated, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding
 		FROM messages 
 		WHERE topic = ? AND time >= ? AND published = 1
 		ORDER BY time, id
 	`
 	selectMessagesSinceTimeIncludeScheduledQuery = `
-		SELECT mid, time, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding
+		SELECT mid, time, updated, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding
 		FROM messages 
 		WHERE topic = ? AND time >= ?
 		ORDER BY time, id
 	`
 	selectMessagesSinceIDQuery = `
-		SELECT mid, time, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding
+		SELECT mid, time, updated, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding
 		FROM messages 
 		WHERE topic = ? AND id > ? AND published = 1 
 		ORDER BY time, id
 	`
 	selectMessagesSinceIDIncludeScheduledQuery = `
-		SELECT mid, time, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding
+		SELECT mid, time, updated, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding
 		FROM messages 
 		WHERE topic = ? AND (id > ? OR published = 0)
 		ORDER BY time, id
 	`
 	selectMessagesDueQuery = `
-		SELECT mid, time, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding
+		SELECT mid, time, updated, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding
 		FROM messages 
 		WHERE time <= ? AND published = 0
 		ORDER BY time, id
 	`
+	selectMessageByIDQuery = `
+		SELECT mid, time, updated, topic, message, title, priority, tags, click, attachment_name, attachment_type, attachment_size, attachment_expires, attachment_url, attachment_owner, encoding
+		FROM messages 
+		WHERE topic = ? AND mid = ?
+	`
 	updateMessagePublishedQuery     = `UPDATE messages SET published = 1 WHERE mid = ?`
 	selectMessagesCountQuery        = `SELECT COUNT(*) FROM messages`
 	selectMessageCountForTopicQuery = `SELECT COUNT(*) FROM messages WHERE topic = ?`
@@ -232,6 +239,7 @@ func (c *messageCache) AddMessage(m *message) error {
 		insertMessageQuery,
 		m.ID,
 		m.Time,
+		m.Updated,
 		m.Topic,
 		m.Message,
 		m.Title,
@@ -250,6 +258,28 @@ func (c *messageCache) AddMessage(m *message) error {
 	return err
 }
 
+func (c *messageCache) UpdateMessage(m *message) error {
+	if m.Event != messageEvent {
+		return errUnexpectedMessageType
+	}
+	if c.nop {
+		return nil
+	}
+	tags := strings.Join(m.Tags, ",")
+	_, err := c.db.Exec(
+		updateMessageQuery,
+		m.Updated,
+		m.Message,
+		m.Title,
+		m.Priority,
+		tags,
+		m.Click,
+		m.Topic,
+		m.ID,
+	)
+	return err
+}
+
 func (c *messageCache) Messages(topic string, since sinceMarker, scheduled bool) ([]*message, error) {
 	if since.IsNone() {
 		return make([]*message, 0), nil
@@ -393,16 +423,31 @@ func (c *messageCache) AttachmentsExpired() ([]string, error) {
 	return ids, nil
 }
 
+func (c *messageCache) Message(topic, id string) (*message, error) {
+	rows, err := c.db.Query(selectMessageByIDQuery, topic, id)
+	if err != nil {
+		return nil, err
+	}
+	messages, err := readMessages(rows)
+	if err != nil {
+		return nil, err
+	} else if len(messages) == 0 {
+		return nil, errors.New("not found")
+	}
+	return messages[0], nil
+}
+
 func readMessages(rows *sql.Rows) ([]*message, error) {
 	defer rows.Close()
 	messages := make([]*message, 0)
 	for rows.Next() {
-		var timestamp, attachmentSize, attachmentExpires int64
+		var timestamp, updated, attachmentSize, attachmentExpires int64
 		var priority int
 		var id, topic, msg, title, tagsStr, click, attachmentName, attachmentType, attachmentURL, attachmentOwner, encoding string
 		err := rows.Scan(
 			&id,
 			&timestamp,
+			&updated,
 			&topic,
 			&msg,
 			&title,
@@ -438,6 +483,7 @@ func readMessages(rows *sql.Rows) ([]*message, error) {
 		messages = append(messages, &message{
 			ID:         id,
 			Time:       timestamp,
+			Updated:    updated,
 			Event:      messageEvent,
 			Topic:      topic,
 			Message:    msg,
diff --git a/server/server.go b/server/server.go
index 0e81cb63..0347e266 100644
--- a/server/server.go
+++ b/server/server.go
@@ -55,9 +55,10 @@ type handleFunc func(http.ResponseWriter, *http.Request, *visitor) error
 
 var (
 	// If changed, don't forget to update Android App and auth_sqlite.go
-	topicRegex             = regexp.MustCompile(`^[-_A-Za-z0-9]{1,64}$`)               // No /!
-	topicPathRegex         = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}$`)              // Regex must match JS & Android app!
-	externalTopicPathRegex = regexp.MustCompile(`^/[^/]+\.[^/]+/[-_A-Za-z0-9]{1,64}$`) // Extended topic path, for web-app, e.g. /example.com/mytopic
+	topicRegex             = regexp.MustCompile(`^[-_A-Za-z0-9]{1,64}$`)                  // No /!
+	topicPathRegex         = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}$`)                 // Regex must match JS & Android app!
+	updateTopicPathRegex   = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}/[A-Za-z0-9]{12}$`) // ID length must match messageIDLength & util.randomStringCharset
+	externalTopicPathRegex = regexp.MustCompile(`^/[^/]+\.[^/]+/[-_A-Za-z0-9]{1,64}$`)    // Extended topic path, for web-app, e.g. /example.com/mytopic
 	jsonPathRegex          = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}(,[-_A-Za-z0-9]{1,64})*/json$`)
 	ssePathRegex           = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}(,[-_A-Za-z0-9]{1,64})*/sse$`)
 	rawPathRegex           = regexp.MustCompile(`^/[-_A-Za-z0-9]{1,64}(,[-_A-Za-z0-9]{1,64})*/raw$`)
@@ -279,7 +280,7 @@ func (s *Server) handleInternal(w http.ResponseWriter, r *http.Request, v *visit
 		return s.handleOptions(w, r)
 	} else if (r.Method == http.MethodPut || r.Method == http.MethodPost) && r.URL.Path == "/" {
 		return s.limitRequests(s.transformBodyJSON(s.authWrite(s.handlePublish)))(w, r, v)
-	} else if (r.Method == http.MethodPut || r.Method == http.MethodPost) && topicPathRegex.MatchString(r.URL.Path) {
+	} else if (r.Method == http.MethodPut || r.Method == http.MethodPost) && (topicPathRegex.MatchString(r.URL.Path) || updateTopicPathRegex.MatchString(r.URL.Path)) {
 		return s.limitRequests(s.authWrite(s.handlePublish))(w, r, v)
 	} else if r.Method == http.MethodGet && publishPathRegex.MatchString(r.URL.Path) {
 		return s.limitRequests(s.authWrite(s.handlePublish))(w, r, v)
@@ -390,7 +391,22 @@ func (s *Server) handleFile(w http.ResponseWriter, r *http.Request, v *visitor)
 }
 
 func (s *Server) handlePublish(w http.ResponseWriter, r *http.Request, v *visitor) error {
-	t, err := s.topicFromPath(r.URL.Path)
+	t, messageID, err := s.topicAndMessageIDFromPath(r.URL.Path)
+	if err != nil {
+		return err
+	}
+	updated := messageID != ""
+	var m *message
+	if updated {
+		m, err = s.messageCache.Message(t.ID, messageID)
+		if err != nil {
+			return err //errors.New("message does not exist")
+		}
+		m.Updated = time.Now().Unix()
+	} else {
+		m = newDefaultMessage(t.ID, "")
+	}
+	cache, firebase, email, unifiedpush, err := s.parsePublishParams(r, v, m)
 	if err != nil {
 		return err
 	}
@@ -398,11 +414,6 @@ func (s *Server) handlePublish(w http.ResponseWriter, r *http.Request, v *visito
 	if err != nil {
 		return err
 	}
-	m := newDefaultMessage(t.ID, "")
-	cache, firebase, email, unifiedpush, err := s.parsePublishParams(r, v, m)
-	if err != nil {
-		return err
-	}
 	if err := s.handlePublishBody(r, v, m, body, unifiedpush); err != nil {
 		return err
 	}
@@ -430,8 +441,14 @@ func (s *Server) handlePublish(w http.ResponseWriter, r *http.Request, v *visito
 		}()
 	}
 	if cache {
-		if err := s.messageCache.AddMessage(m); err != nil {
-			return err
+		if updated {
+			if err := s.messageCache.UpdateMessage(m); err != nil {
+				return err
+			}
+		} else {
+			if err := s.messageCache.AddMessage(m); err != nil {
+				return err
+			}
 		}
 	}
 	w.Header().Set("Content-Type", "application/json")
@@ -447,6 +464,10 @@ func (s *Server) handlePublish(w http.ResponseWriter, r *http.Request, v *visito
 
 func (s *Server) parsePublishParams(r *http.Request, v *visitor, m *message) (cache bool, firebase bool, email string, unifiedpush bool, err error) {
 	cache = readBoolParam(r, true, "x-cache", "cache")
+	if !cache && m.Updated != 0 {
+		return false, false, "", false, errors.New("message updates must be cached")
+	}
+	// TODO more restrictions
 	firebase = readBoolParam(r, true, "x-firebase", "firebase")
 	m.Title = readParam(r, "x-title", "title", "t")
 	m.Click = readParam(r, "x-click", "click")
@@ -888,16 +909,20 @@ func (s *Server) handleOptions(w http.ResponseWriter, _ *http.Request) error {
 	return nil
 }
 
-func (s *Server) topicFromPath(path string) (*topic, error) {
+func (s *Server) topicAndMessageIDFromPath(path string) (*topic, string, error) {
 	parts := strings.Split(path, "/")
-	if len(parts) < 2 {
-		return nil, errHTTPBadRequestTopicInvalid
+	if len(parts) != 2 && len(parts) != 3 {
+		return nil, "", errHTTPBadRequestTopicInvalid
 	}
 	topics, err := s.topicsFromIDs(parts[1])
 	if err != nil {
-		return nil, err
+		return nil, "", err
 	}
-	return topics[0], nil
+	messageID := ""
+	if len(parts) == 3 && len(parts[2]) == messageIDLength {
+		messageID = parts[2]
+	}
+	return topics[0], messageID, nil
 }
 
 func (s *Server) topicsFromPath(path string) ([]*topic, string, error) {
diff --git a/server/types.go b/server/types.go
index 6594f050..d003df2c 100644
--- a/server/types.go
+++ b/server/types.go
@@ -30,7 +30,9 @@ type message struct {
 	Attachment *attachment `json:"attachment,omitempty"`
 	Title      string      `json:"title,omitempty"`
 	Message    string      `json:"message,omitempty"`
-	Encoding   string      `json:"encoding,omitempty"` // empty for raw UTF-8, or "base64" for encoded bytes
+	Encoding   string      `json:"encoding,omitempty"` // Empty for raw UTF-8, or "base64" for encoded bytes
+	Updated    int64       `json:"updated,omitempty"`  // Set if updated, unix time in seconds
+	Deleted    int64       `json:"deleted,omitempty"`  // Set if deleted, unix time in seconds
 }
 
 type attachment struct {
diff --git a/util/util.go b/util/util.go
index e05736fc..90ba4e08 100644
--- a/util/util.go
+++ b/util/util.go
@@ -17,7 +17,7 @@ import (
 )
 
 const (
-	randomStringCharset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+	randomStringCharset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789" // Update updateTopicPathRegex if changed
 )
 
 var (