[Asterisk-Users] sendmail&hostname

[Altus Snyman]

Good day all
I'm just wondering for interest sake
I have a box,hostname=myname.co.za,running sendmail
If I send mail to someuser at myname.co.za it try to deliver to the box,witch 
does not have the mail box.How do I tell sendmail that it should send mail to 
myname.co.za's mailserver.
I know how easy it is to change the name but there's a lot of reasons why we 
can.It is not in the local-hostnames file either.
Thanks
Altus