new administrator: please help me choose news server

[Zhang Weiwu]

Hello. I never did this before, but now I'll setup a mail server in the 
coming weeks. Here is the requirement:

1) the mail server should run both smtp and imap, sending and accepting 
emails
2) mail server should be able to ask for confirm before it deliever 
executables. Or it should be able to reject all emails with Windows 
executable file attached
3) should be albe to extend to handle multi-domains in the future

I don't really understand what part of email server is handled by what 
program. I thought I need a sendmail plus a imap server (cyrus comes out 
in my mind, but I don't know if it should be my choice), is that all?

I'm the kind of lazy guy not to RTFM, but I need direction guide, 
suggestion from you so that I know what the f**k manual to read:)

Thank you!