[lug] Sendmail issues

I have configured sendmail+dovecot+procmail+mailscanner.
I want my mail server with trhe following features
1. I would like to block the emails for some(i can do this in relay)
2. I want to block attachments based on the file extensions and file
size. The major capability!!!!
3. Ability to backup mails for every end user.(Suppose, the server
crashes, then what!!!so keep a backup safe.thats my moto)
4. Handle with the TIMEZONES.(this is really useful if u recieve mail
from another country)
5. redirect mails (it can be done in virtusertable/DNS conf)
6. Handling aliases
7. Store the client contacts on the server.

These are just my views.
I want to know where i should start and what i should do?
Any suggestions are welcome.

Thanks in advance

Sailaja Bhandaru