fix(GODT-3041): Fix Invalid Or Missing message signature during send

If we update the address after determining the sender address is
different, we also need to refresh the identity state in order to use
the right encryption keys.

internal/services/smtp/smtp.go

@@ -95,6 +95,11 @@ func (s *Service) smtpSendMail(ctx context.Context, authID string, from string,
 	// If the message contains a sender, use it instead of the one from the return path.
 	if sender, ok := getMessageSender(parser); ok {
 		from = sender
+		fromAddr, err = s.identityState.GetAddr(from)
+		if err != nil {
+			logrus.WithError(err).Errorf("Failed to get identity from sender address %v", sender)
+			return ErrInvalidReturnPath
+		}
 	}
 
 	// Load the user's mail settings.