[exim] mail function doesn´t work....

Hi everybody,
i wonder why i can´t send email through domain email account, example:
user@???, and its weird, because i can send email through
gmail, hotmail, yahoo, etc. i have CPANEL, running exim 4.43, running
on RedHat 9.
Please, give me any suggestion...
I mean this function:
"" #mail user@any-domain """
running as root user.
I already ran exim -bt user@??? and says: unrouteable address.
Thanks in advance ..
Roberto