As you aware that the Version 1.0 of the Outlook REST API was launched in 2015 to provide API access to mail, calendar, contacts, and other data from Exchange Online. Later we came up with Outlook REST API v2.0 and Microsoft Graph, both of which provide richer features, and better performance and reliability than Outlook REST API v1.0. So some technologies become obsolete, because they no longer provide the best way to interact with Office 365 data. Here is our support deprecation policy statement.
So please note that we announced that from November 1st, 2018, we will stop supporting Basic Authentication in Outlook REST API v1.0. Additionally, starting on November 1st, 2019, we will decommission the Outlook REST API v1.0 in favor of Microsoft Graph and Outlook REST API v2.0. This means that new or existing apps will not be able to use Basic Authentication in Outlook REST API v1.0 starting November 1st, 2018 and will not be able to use Outlook REST API v1.0 at all starting November 1st, 2019.
What’s next? If you have been using the Outlook REST v1.0 API in your app, you should plan on transitioning to Microsoft Graph-based Outlook REST APIs to continue accessing Exchange Online data.
Hope this helps.