diff --git a/downstream.go b/downstream.go
index 47f7af4..d80ced5 100644
--- a/downstream.go
+++ b/downstream.go
@@ -250,6 +250,9 @@ func (dc *downstreamConn) readMessages(ch chan<- event) error {
 // This can only called from the user goroutine.
 func (dc *downstreamConn) SendMessage(msg *irc.Message) {
 	if !dc.caps["message-tags"] {
+		if msg.Command == "TAGMSG" {
+			return
+		}
 		msg = msg.Copy()
 		for name := range msg.Tags {
 			supported := false
@@ -274,7 +277,7 @@ func (dc *downstreamConn) marshalMessage(msg *irc.Message, net *network) *irc.Me
 	msg.Prefix = dc.marshalUserPrefix(net, msg.Prefix)
 
 	switch msg.Command {
-	case "PRIVMSG", "NOTICE":
+	case "PRIVMSG", "NOTICE", "TAGMSG":
 		msg.Params[0] = dc.marshalEntity(net, msg.Params[0])
 	case "NICK":
 		// Nick change for another user
@@ -1397,6 +1400,7 @@ func (dc *downstreamConn) handleMessageRegistered(msg *irc.Message) error {
 		if err := parseMessageParams(msg, &targetsStr, &text); err != nil {
 			return err
 		}
+		tags := copyClientTags(msg.Tags)
 
 		for _, name := range strings.Split(targetsStr, ",") {
 			if name == serviceNick {
@@ -1418,14 +1422,15 @@ func (dc *downstreamConn) handleMessageRegistered(msg *irc.Message) error {
 				unmarshaledText = dc.unmarshalText(uc, text)
 			}
 			uc.SendMessageLabeled(dc.id, &irc.Message{
+				Tags:    tags,
 				Command: "PRIVMSG",
 				Params:  []string{upstreamName, unmarshaledText},
 			})
 
+			echoTags := tags.Copy()
+			echoTags["time"] = irc.TagValue(time.Now().UTC().Format(serverTimeLayout))
 			echoMsg := &irc.Message{
-				Tags: irc.Tags{
-					"time": irc.TagValue(time.Now().UTC().Format(serverTimeLayout)),
-				},
+				Tags: echoTags,
 				Prefix: &irc.Prefix{
 					Name: uc.nick,
 					User: uc.username,
@@ -1440,6 +1445,7 @@ func (dc *downstreamConn) handleMessageRegistered(msg *irc.Message) error {
 		if err := parseMessageParams(msg, &targetsStr, &text); err != nil {
 			return err
 		}
+		tags := copyClientTags(msg.Tags)
 
 		for _, name := range strings.Split(targetsStr, ",") {
 			uc, upstreamName, err := dc.unmarshalEntity(name)
@@ -1452,10 +1458,30 @@ func (dc *downstreamConn) handleMessageRegistered(msg *irc.Message) error {
 				unmarshaledText = dc.unmarshalText(uc, text)
 			}
 			uc.SendMessageLabeled(dc.id, &irc.Message{
+				Tags:    tags,
 				Command: "NOTICE",
 				Params:  []string{upstreamName, unmarshaledText},
 			})
 		}
+	case "TAGMSG":
+		var targetsStr string
+		if err := parseMessageParams(msg, &targetsStr); err != nil {
+			return err
+		}
+		tags := copyClientTags(msg.Tags)
+
+		for _, name := range strings.Split(targetsStr, ",") {
+			uc, upstreamName, err := dc.unmarshalEntity(name)
+			if err != nil {
+				return err
+			}
+
+			uc.SendMessageLabeled(dc.id, &irc.Message{
+				Tags:    tags,
+				Command: "TAGMSG",
+				Params:  []string{upstreamName},
+			})
+		}
 	case "INVITE":
 		var user, channel string
 		if err := parseMessageParams(msg, &user, &channel); err != nil {
diff --git a/irc.go b/irc.go
index 50a22c1..8fae660 100644
--- a/irc.go
+++ b/irc.go
@@ -274,6 +274,16 @@ func parseMessageParams(msg *irc.Message, out ...*string) error {
 	return nil
 }
 
+func copyClientTags(tags irc.Tags) irc.Tags {
+	t := make(irc.Tags, len(tags))
+	for k, v := range tags {
+		if strings.HasPrefix(k, "+") {
+			t[k] = v
+		}
+	}
+	return t
+}
+
 type batch struct {
 	Type   string
 	Params []string
diff --git a/upstream.go b/upstream.go
index 1ea282f..60f75fc 100644
--- a/upstream.go
+++ b/upstream.go
@@ -320,14 +320,20 @@ func (uc *upstreamConn) handleMessage(msg *irc.Message) error {
 			Params:  msg.Params,
 		})
 		return nil
-	case "NOTICE", "PRIVMSG":
+	case "NOTICE", "PRIVMSG", "TAGMSG":
 		if msg.Prefix == nil {
 			return fmt.Errorf("expected a prefix")
 		}
 
 		var entity, text string
-		if err := parseMessageParams(msg, &entity, &text); err != nil {
-			return err
+		if msg.Command != "TAGMSG" {
+			if err := parseMessageParams(msg, &entity, &text); err != nil {
+				return err
+			}
+		} else {
+			if err := parseMessageParams(msg, &entity); err != nil {
+				return err
+			}
 		}
 
 		if msg.Prefix.Name == serviceNick {
@@ -341,7 +347,7 @@ func (uc *upstreamConn) handleMessage(msg *irc.Message) error {
 
 		if msg.Prefix.User == "" && msg.Prefix.Host == "" { // server message
 			uc.produce("", msg, nil)
-		} else { // regular user NOTICE or PRIVMSG
+		} else { // regular user message
 			target := entity
 			if target == uc.nick {
 				target = msg.Prefix.Name
@@ -1274,8 +1280,6 @@ func (uc *upstreamConn) handleMessage(msg *irc.Message) error {
 				})
 			})
 		}
-	case "TAGMSG":
-		// TODO: relay to downstream connections that accept message-tags
 	case "ACK":
 		// Ignore
 	case irc.RPL_NOWAWAY, irc.RPL_UNAWAY:
@@ -1487,6 +1491,15 @@ func (uc *upstreamConn) readMessages(ch chan<- event) error {
 	return nil
 }
 
+func (uc *upstreamConn) SendMessage(msg *irc.Message) {
+	if !uc.caps["message-tags"] {
+		msg = msg.Copy()
+		msg.Tags = nil
+	}
+
+	uc.conn.SendMessage(msg)
+}
+
 func (uc *upstreamConn) SendMessageLabeled(downstreamID uint64, msg *irc.Message) {
 	if uc.caps["labeled-response"] {
 		if msg.Tags == nil {