Since upgrading, my Mail.app no longer opens. When I open it, I receive a message saying do you want to reopen windows? Regardless of what option I choose, it hangs with the rainbow beach ball indefinitely and does not do anything. I have tried deleting the plist file and restarting the computer. Any suggestions? I'm using Outlook for now, but even the latest version is very slow and annoying to use. Alternatively, any free apps that work with Office 365 in case I cannot get Mail.app to work? (Don't suggest CloudMagic or Newton, lousiest business ever).