[CentOS] query on sendmail issues

Dear All,

i have installed Centos 4.5 and is working perfectly fine me actually a
novice and is my first time with centos though have experince with redhat

i do have a few queries..


1) i dont see /usr/src/redhat/BUILD and the other 4 directories..
namely RPMS, SOURCES, SPECS, SRPMS
so basically how do i install /src.rpm files

i have installed sendmail ver 13 with mailscanner n spammassassin n is
working fine..

but like to know a few things

its absoulutly new domain n mails sent to hotmail and yahoo go to junk
mail folder..

i guess implemnting DKIM for sendmail will help ..
but wa snot gettin enogh details on how to implement this...


appreciate if someone can hrlp me and detail me some steps or give me so
possible links tht gonna be of help


thnks and apprecite

Regards

simon