Q I'm setting up a web/mail server. I'm a novice, so what would you recommend as a user friendly, secure Linux OS and web/mail server software with an easy interface for sharing Windows files? Preferably something with a large user manual, it will be used in a small office.
A Oh dear, all I can say with any certainty is that whatever I recommend will produce howls of disagreement from those who favour other distributions. While the popular distributions are general purpose and all suitable for desktop, workstation or server use, there are a number of smaller distributions that are specifically designed for the sort of thing you want to do. One such distro is ClarkConnect (www.clarkconnect.com). While ClarkConnect is best known as an Internet gateway, a means of connecting a network to the Internet, with suitable content filters and access controls, it can also be used as an intranet server.
As you admit to being a novice and will be using this in a commercial environment, I strongly suggest that you consider taking one of the paid for versions, although you could install a free version first to try it out. ClarkConnect provide Community, Office and Enterprise versions. The Community Edition is completely free while the other two have 30-day trial periods. The paid-for editions offer extra features and, most importantly, support. ClarkConnect needs a keyboard and monitor attached to the server for installation and basic initial configuration, after that everything is done via its web interface.
Administration is done over a secure SSL connection using a non-standard port, you need to know the IP address of the ClarkConnect server, which you can see after logging in with the root password, then you can use any web browser on the network to connect to http://ip-address:81. A Linux installation is as secure as you make it. Using a server-oriented distro with a minimal number of packages helps, but it is still up to you do ensure that software is kept up to date, use the Software Install menu in the administration interface, and that you set up a firewall.
The firewall is included and set up from your browser. Even if you are not using this as an Internet gateway, it is wise to protect the services and data on the box with its own firewall, in addition to whatever you have on your Internet gateway or router. It is also possible to use a general purpose distro for this task, by opting to install server instead of desktop packages when you install it. Most distros include the excellent Webmin program that can be used to administer servers with a web browser, but for a separate server machine, especially when your experience is limited, a purpose-built distro is probably the best choice. While ClarkConnect doesn't come with a printed manual, there's plenty of documentation on the website, both in the detailed user guide the various How Tos. There are also user forums for peer group help.