Backups. Check out http://www.linuxquestions.org/bookmarks/tags/backup
. For general network backup of multiple machines, I like Amanda
. Rsync has it's place, and I use it. But all my department backup servers run Amanda
. Once it is configured and running, it just works, and it stays out of your way when it's not running. You can run backups to tape, to disk space, to the cloud.
I build critical applications (like Amanda) from source. Last I checked the ubuntu package was more than a couple of years out of date. Building from source is pretty simple, and there are howtos on the wiki -- http://wiki.zmanda.com/index.php/Quick_start
, for example.
Mail. I use a combination of Sendmail, miltergreylist, mimedefang, spamassassin, and uw-imap. It's not the easiest setup to configure and might not suit your situation. I happen to share responsibilities with a senior admin who is an expert on sendmail, and we serve hundreds of users with tens of thousands of emails a day. Blocking spam without blocking legitimate email becomes a major endeavor. You'll have to keep an eye on things. Don't be an open relay. Don't accept mail except for actual real local user accounts. Require smtp auth and use ssl or tls for all connections. Use account names that aren't simple first names, and ask your users to avoid openly publishing their emails on the web. Lots of other things involved in fighting spam, but those are some of the simplest recommendations. Greylisting knocks out a large portion of spam.