Hi ALInux
if i understand you correct you are trying to send mails from your local mailserver (postfix,sendmail,etc) at home or office to send mails to hotmail, gmail etc...
in order to not get blocked or to get on the spam lists... xbl-sbl etc
you will need:
1.correct dns entries
A record and PTR record that are pointing back to you...
if i remember right maybe also SPF entry...
2. if you would like to receive mails you will need MX records pointing to your mailserver...
in short... your mails are going to the junk folder because you do not have correct DNS entries and maybe you are using a dynamic ip range...
good luck...
Yaniv Ferszt
oh and about the other thing...
you will need to configure masquerade... on your mail server...
so if you send a mail from root@localhost it will masquerade it to
root@your_domain.com