Microsoft has announced that RPC over HTTP will be deprecated on October 31, 2017 for Office 365 / Exchange Online. Simply put, Microsoft will no longer support connections to the Office 365 / Exchange Online platform via RPC over HTTP as of October 31, 2017. Instead, Microsoft will rely on the modern MAPI over HTTP.
If you are running Outlook 2007 for Windows to connect to Office 365 / Exchange Online, you will need to upgrade to a newer version of Outlook which supports MAPI over HTTP. The current version is Outlook 2016. Outlook 2007 does not support MAPI over HTTP and as such, starting October 31st, you will no longer be able to use it to connect to Office 365 / Exchange Online.
Microsoft also recommends that users running Outlook 2010, 2013 and 2016 install the latest updates for their respective Outlook applications to ensure support for MAPI over HTTP. This change only affects Outlook for Windows and does not affect Outlook for Mac, Outlook for iOS, Outlook for Android, Outlook for Windows Mobile or Outlook for Web.
For full details on this change, go to: https://support.microsoft.com/en-us/help/3201590/rpc-over-http-deprecated-in-office-365-on-october-31,-2017
TIP: If you are unsure how this change may affect you or your company, consult with an IT professional or your company’s IT department.