Existing clients that are connecting via RPC/HTTP will continue to connect after that date. The KB article (3201590) has updated information.
What exactly does the announcement that Microsoft is deprecating RPC over HTTP support in Office 365 mean for Outlook.com and Office 365 Exchange Online subscribers?
It means that as of October 31, 2017, Outlook for Windows will only be able to connect to Office 365 servers using MAPI over HTTPS protocol.
Anyone using Outlook 2010 and above will need to have the December 8, 2015 update for Office installed to continue to connect to Outlook.com or an Office 365 mailbox. Outlook 2010 users will also need to have Office 2010 Service Pack 2, or greater, installed; Outlook 2013 needs Office 2013 Service Pack 1. Office 365 subscribers should have all necessary updates automatically installed.
Administrators who disabled MAPI over HTTPS support in the registry will need to delete the MapiHttpDisabled value from the registry. This value is in the registry (on desktop computers) at
Anyone still using Outlook 2007 will no longer be able to connect to Outlook.com using Exchange services (after October 31 2017). These users will either need to upgrade to the current version of Office or Outlook, use POP3 or IMAP (these do not support calendar or contact sync), or use Outlook on the web.
Outlook apps for devices and Outlook 2016 for Mac are not affected.
While organizations still using Outlook 2007 will need much of the next 11 months to plan their upgrades, I recommend Outlook.com users connecting with Outlook 2007 upgrade to Office 365 software when buying a new computer, otherwise wait to upgrade in the fall.