Microsoft will end all support for Windows XP on 8th April 2014 — please upgrade all Windows XP workstations to Windows 7 or Windows 8 prior to this date. 

While Office 365 will not block connections from fully patched Windows XP computers after 8th April 2014, connectivity to the service will be at risk. Windows XP workstations that have not deployed all service packs and automatic updates run an even higher risk of Office 365 connectivity issues after support for Windows XP ends.

If you experience a technical problem connecting to Office 365 from a Windows XP machine after 8th April 2014, Microsoft Customer Support and Service will need you to reproduce the problem on a supported operating system.