How come i cannot change my sbc address to a yahoo adress/it says it is taken but i only get mailer daemons?

Question

if i get mailer daemons back isnt that an indication that there is no such address/precisely what the daemons reasons were/if this is the case why cant i use my old address and why is it telling me that this yahoo name is not available

Answer 1

It was in use at one time and got deactivated so the ID is no longer available.