For Office 2011 for Mac and Outlook app for iPhone for Office 365, I am forced to reauthenticate (login) several times a week for multiple email accounts, both Office 365 and Outlook.com  Not only is this behavior annoying, it is a big time waster. I am getting to the point of moving to another email service if this problem is not solved. When I asked GoDaddy about this (O365 reseller), they suggested I use the native Apple email client!