I've used thunderbird for years. For business stuff though I have a Zimbra install which gives me a credible web client, plus activesync and an MAPI interface for the one Outlook user left.
I've used Linux on the desktop since about 96, but I keep a few windows VMs around for Office, AutoCAD and Revit. I find windows behaves better and runs faster in a VM than on the bare metal, plus I can deny it network access to the outside world. No phone home or updates without my explicit say-so. I can also upgrade the underlying machines without worrying about license keys or activation issues, plus duplicate/snapshot for testing stuff without crapping-up the windows install.
Unfortunately I need Office for collaboration, but I use Libreoffice for pretty much anything I can get away with.
My main office VM is still Office 2007 on XP 32 bit. I've had to upgrade to Windows 8.1 64 bit for the Cad VM, but it's cut and shut down to a minimum footprint.
I have a very strong dislike for pretty much anything Microsoft, but unfortunately it's still pretty essential if you collaborate with other organizations. I reserve a special pit in hell for Outlook, but at least with everything on the Zimbra server a "delete/re-install" takes a matter of minutes with no config or data loss.

