"Kloxo (Previously Lxadmin) The most flexible software on this planet. From Kloxo HostInaBox, World's lightest and the most efficient webhosting platform, to Kloxo Enterprise, which can manage 100s of thousands of domains on hundreds of servers."
If you're looking to configure mail from your slicehost and you do go with the Google Apps option (that's what I use), you might like to have a look at this guide to getting sSMTP working with Google:
I can't recommend sSMTP enough to anyone that doesn't want to maintain a mail server. All UNIX systems should be able to send mail and this is very much still the case on modern Linux systems, but this is often overlooked.
http://news.ycombinator.com/item?id=648806 (LxLabs boss found hanged after vuln wipes websites) same story on the register
and
http://news.ycombinator.com/item?id=648788 (Hack wipes out data for 100,000 sites)
and
http://news.ycombinator.com/item?id=646451 (VAServ 'hacked' - all web sites and hosted VMs down)