postfix help

i have installed a local intranet dns server
testing was o.k

i am installing a local intranet mailserver with postfix.
i am getting a lots of confusion.

the name of my machine..i have named it to Mailserver....

when i do postfix start..it tells me ..."failed"

i have checked the var/log/maillog....
and the fisrt error is warning ; My hostname mailserver is not a fully qualified name-set my hostname in main.cf

but this i have already done!!

plz give me some troubleshooting tips and guideline