The bottom line is: Office 365 is not designed to work with Internet Explorer [IE] 8, and the user experience in Outlook Web Access [OWA] may be compromised, especially when used on Windows XP and/or with low memory machines. Office 365 will not offer code fixes to resolve problems encountered when using IE8, and new Office 365 experiences will likely not work at all.
Office 365 is no longer ending all support for IE8 on 8 April 2014, but both the user and support experience will be limited. After 8 April 2014, IE8 users:
• Will not be deliberately prevented from connecting to the service;
• Will not receive code fixes for bugs related to IE8. Security fixes will be released as needed;
• May only use OWA Light (this does not apply to Office 365 Dedicated);
• Should expect that the quality of other Office 365 user experiences will diminish over time.
While Office 365 Customer Support and Service will attempt to assist customers with IE8-related problems, the only solution to a particular problem may be to upgrade to a modern browser.
The recommended browser is, at this stage, IE9 with at least MS12-037: Cumulative Security Update for Internet Explorer: June 12, 2012 installed. However, IE10 or later is strongly recommended. This is because, similarly to IE8, Office 365 does not offer code fixes to resolve problems encountered when using IE9, the quality of the user experience will likely diminish over time, and that some new Office 365 experiences might not work at all.
As such, to reiterate, IE10 or later is strongly recommended.