Hello,
If I want to have the ability to add a new branch for every negative response, included the 6xx (and despite what is written in the RFC3261), where should I change?
It is enough to remove the following code in t_should_relay_response function?

  783           if (new_code>=600) {
  784                   /* this is a winner and close all branches */
  785                   which_cancel( Trans, cancel_bitmap );
  786                   picked_branch=branch;
  787                   /* no more new branches should be added to this transaction */
  788                   Trans->flags |= T_NO_NEW_BRANCHES_FLAG;

**********************************************************************
The information in this message is confidential and may be legally
privileged. It is intended solely for the addressee. Access to this message
by anyone else is unauthorized. If you are not the intended recipient, any
disclosure, copying, or distribution of the message, or any action or
omission taken by you in reliance on it, is prohibited and may be unlawful.
Please immediately contact the sender if you have received this message inerror.

**********************************************************************