The Harvard Business Review released a great adoption article in December 2017 titled To Get People to Change, Make Change Easy.

The user adoption article explains how nominal decisions that users make every day (e.g. what technology to use) are often driven by the path of least resistance. In order to drive adoption of a specific use case or technology, product teams should identify the natural friction (aka resistance) in choosing one path or process over another. Reducing the friction lowers the barrier to entry, enabling your users to more easily adopt new processes and behaviors.

You can utilize this same theory to limit or stop behaviors that are no longer desired. To deter specific user behaviors (e.g. using a legacy system rather than a new Office 365 capability), introduce more friction into the old tool or process. By making the old tool harder to use, you open the door to new adoption behaviors.