There are a lot of companies out there now that offer email hosting, but the main problem that you will find with them is that they charge a monthly fee for each mailbox, which can add up to quite a yearly sum if you want to add a lot of mailboxes.
When it comes to the remote support of client machines, there are quite a few options available, with each of them having their advantages and disadvantages.
I have been setting up VPN's on OS X server for a while and one thing that I did like about configuring them, was how easy it was to add and remove users.
It seems as if automated website attacks by compromised machines is something that all webmasters have to think about, because I made the mistake of installing an old version of Wordpress and was surprised to find that my server was now suddenly making a lot of outgoing connections.
When I set up a server using one of the free unix based systems, I will usually configure them so that they will send an email message if there is a problem with the RAID system. Recently the server of a photographer client did send a message saying that one of the disks had a problem.
A few years ago the chances of someone recommending open source software for business use would be very small. There were a few applications that could have been used, but you would have ended up with a mix of software and the chances of compatibility problems would be quite high.
With the way that most popular server systems are going of late, with higher and higher hardware requirements, it is getting a lot more difficult for small businesses to find a reasonable deal when they want to set up a server at their office.