I had a couple of questions from users still using Outlook 2007, wondering if they would be able to use it with Office 365 Exchange Online.
As long as all Outlook 2007 updates are installed, you can use Outlook 2007 to connect to Office 365 Exchange Online or the new Outlook.com (hosted on Office 365 infrastructure) as a Microsoft Exchange account. The quality of the connection may degrade as the servers receive updates that Outlook 2007 doesn't support, but it will work for the basic sync.
You’ll obviously have a better experience if you are using Outlook 2013 or Outlook 2016, and you won’t be able to use the newer Exchange 2016 features that are available to Outlook 2013 and Outlook 2016 users, but the important things - your email, calendar, contacts, and tasks - will sync and the features you are familiar with will continue to work.
The RPC over HTTPS protocol was supposed to be disabled for Office 365 and Outlook.com accounts at the end of October 2017 but is currently on reprieve. For more information, see Deprecation of RPC over HTTP in Office 365 (and Outlook.com) for more information.
Another important date is October 10, 2017, which marks the end of the Extended support period. While this won’t affect ordinary users and the Office applications will continue to work, it does mean that security updates are unlikely to continue past that date.