You are checking mail in a MIcrosoft account (Hotmail / Live / Outlook)? Thunderbird doesn't use Outlook 2007 (the Outlook that is part of Microsoft Office) to send or receive email. However, I wouldn't uninstall it, for two reasons: * You may discover there's some data that Thunderbird didn't get that you need to export manually; * Some email or calendar related features of other MS Office applications could be affected if you uninstall Outlook. I suggest just letting Outlook 2007 sit there unused. (You could get rid of its icon from the desktop so it's out of sight.) As for Outlook online, you will always have that available as a backup when you need to check your Microsoft mailbox through the browser. You may not need it very often, but I don't think there's anything to delete there.