You might have been receive prompts from Dynamics to begin removing the Outlook 365 for Outlook.
The naming convention on these apps is fun, because the official names are almost identical resulting in nearly 100% confusion about which one you’re actually talking about.
To be clear, Dynamics 365 App for Outlook is an integrated App within Outlook itself, meaning you will have a pane that contains a window into Dynamics itself. It’s also the newer and planned for support in future. The Dynamics 365 for Outlook was a COM addin, meaning you installed it into the Outlook manually and got access to the local system (allowing offline mode).
If you need visuals, Dynamics 365 for Outlook (old) looked like this,

Whilst Dynamics 365 App for Outlook (new) looks like this,

Whats the difference?
The following info is shamelessly stolen from a Microsoft document, I found when researching this post, but it was too clear not to reuse.
Feature | Outlook Addin (COM) | Dynamics 365 App for Outlook |
---|---|---|
Technology | Based on COM/VSTO, a legacy Outlook integration model without any active development Based on legacy web client (deprecated) Based on Unified Interface Depends on SQL Server Compact 4.0 (End of extended support in 2021) | Cross Platform (Web based JS/HTML) Based in Unified Interface No dependencies on end-of-life features |
Performance | Known to affect the client machine’s performance | Lightweight integration |
Client(s) | Windows + Outlook Desktop | Windows & Mac OS, Outlook Web Access, Smartphone & tablet (iOS/Android) |
Deployment | Client Installation Expensive to deploy and support | Centralized deployment and distribution |
Security | Full access in client machine/native code | Sandboxed, access through standard Office.js AP |
When do I have to upgrade?
The suggested timeline from Microsoft is to begin upgrading now.
The old addin is officially deprecated as of March 2020 with a statement customers must migrate before October 1st 2020. After this point, Microsoft will now provide any support or security updates, although its unclear as of now if it will continue working if your business accepts these risks. (Not recommended!)
How do I upgrade?
To get this setup has a few prerequisites. First, you need to identify if your current Servers are at the minimum versions. Your exchange server ideally should be 2016 ir Exchange Online and your Outlook Clients should be Outlook 2016 (C2R) or 2019.
You will need to have Server Side Synchronisation set up and be using Unified Interface within Dynamics itself. Upgrading servers, setting up sync or Unified Interface is out of scope of this post.
Assuming you have all of these in place though, its pretty easy to turn on.
Go to Settings>System>Dynamics 365 App for Outlook and review the page to see if your system is set up. If its not, you will be prompted what you need to do to proceed.
Make sure you check the ‘Automatically add Dynamics 365 App for Outlook to all eligible users’. This allows the Exchange server to add the app without needing to install anything on the users machine.
Make sure you User profiles in Dynamics are set up and authorised to interface with your Exchange server. Approve the mail (this requires Office Admin or Exchange Admin privileges). Then test and Enable it to make sure its syncing correctly.

Assign the user the ‘Dynamics 365 App for Outlook User’ role.
This should allow your system to do its magic! It can take a few minutes to push through and update, but once it has, you can easily set up and manage your users by repeating the two steps of enable/test their mailbox, then add the role.
Good luck with your upgrades!