For login credentials:
user@domain.com_username2 wont work ever as .com_username2 is no toplevel domain any dns knows about. use proper json formated configs with "-c config.json" or use the commands "-o domain.com:port -u username -p password" and it might work
Yes it will. For deepbit, "
user@domain.com_username2" is the complete username, not the URL (as suggested by the lack of protocol).