Does address of external parties added in Global Address List need seperate CAL.

hi,

I want to add the email address of my Service Provider { i.e. my domain is abc.com and I want to add my service provider mail id 123 at xyz . com }  in the Global Address List on my exchange server. The user 123@xyz .com will never access my server Directly or indirectly. still I have to buy CAL for 123 at xyz . com id ?

Regards,

Amit