diff --git a/internal/bridge/send_test.go b/internal/bridge/send_test.go
index ff5ede21..7f009f61 100644
--- a/internal/bridge/send_test.go
+++ b/internal/bridge/send_test.go
@@ -101,7 +101,7 @@ func TestBridge_Send(t *testing.T) {
 			defer recipientIMAPClient.Logout() //nolint:errcheck
 
 			// Sender should have 10 messages in the sent folder.
-			// Recipient should have 0 messages in inbox.
+			// Recipient should have 10 messages in inbox.
 			require.Eventually(t, func() bool {
 				sent, err := senderIMAPClient.Status(`Sent`, []imap.StatusItem{imap.StatusMessages})
 				require.NoError(t, err)
diff --git a/internal/user/smtp.go b/internal/user/smtp.go
index 3938a3c7..702dfd24 100644
--- a/internal/user/smtp.go
+++ b/internal/user/smtp.go
@@ -174,7 +174,11 @@ func sendWithKey( //nolint:funlen
 	to []string,
 	message message.Message,
 ) (proton.Message, error) {
-	parentID, err := getParentID(ctx, client, authAddrID, addrMode, message.References)
+	references := message.References
+	if message.InReplyTo != "" {
+		references = append(references, message.InReplyTo)
+	}
+	parentID, err := getParentID(ctx, client, authAddrID, addrMode, references)
 	if err != nil {
 		return proton.Message{}, fmt.Errorf("failed to get parent ID: %w", err)
 	}