Before upgrading our environment to Dynamics 365 CE, we need to review the customization to check whether any unsupported customization is available in the customer environment. Unsupported customization can stop our upgrade process. Apart from that, we also need to review Microsoft or other vendor solutions that we have used for our customers to make sure they are still available for Dynamics 365 CE versions. Similarly, we may be using community solutions for an earlier version, so we need to check whether a similar solution is available that is compatible with Dynamics 365 CE. If not, we may need to develop an equal solution for Dynamics 365 CE.

The following is the list of customizations that are deprecated in Dynamics 365 CE v9:

• Voice of the Customer (VoC): This was used for creating a survey in Dynamics CRM, but this solution is deprecated in Dynamics 365 CE. Now, we have a different solution, called Microsoft Forms Pro, which can be used to create a survey. You can find more details about Microsoft Forms Pro here: https://formspro.microsoft.com/en-us/. We need to replace the survey that we created with Microsoft Forms Pro.
• The Blackberry app: Microsoft has deprecated the Blackberry app for Dynamics 365 CE. Although Microsoft will continue to provide security and other updates for the Blackberry app, it will soon be removed from the app stores. So, if our customer is using a Blackberry app, we need to plan to migrate them to the Dynamics 365 CE for phones app.
• The Outlook add-in: Microsoft has deprecated the Outlook add-in for Dynamics 365 CE, which also includes features such as offline mode and synchronization in Dynamics 365 for Outlook. So, we need to plan to migrate our Outlook app customers to the Dynamics 365 CE app for Outlook. This app provides more features; for example, it's a user-responsive design. We can drill down to view record details within the app; it provides contextual information from Dynamics 365 CE. Now, it's easy to associate an Outlook email or appointment with a Dynamics 365 CE record, with a single click. This app works with server-side sync.

• Service scheduling: If you are a service-providing company using service scheduling under a custom service module, you need to start planning on using the new Universal Resource Scheduling (URS), which is available in Unified Interface.
• Dialog changes: Dialogs provide us with the option to design multi-screen processes where we can provide user output based on their inputs. Dialogs are also used widely by many service-based customers to process requirements based on user queries. But dialogs are deprecated in Dynamics 365 CE, so we need to plan on using a business process flow, or we need to design canvas apps to implement our requirements. However, keep in mind canvas app embedding to an entity form is only available for Dynamics 365 CE Online.
• Contract entities: All contract entities, such as Contracts, Contract Line Items, and Contract Templates are deprecated in Dynamics 365 CE. If your customer is using these entities, we need to implement their requirements using Entitlement entities in Dynamics 365 CE.
• Standard SLAs: In the earlier version of Dynamics CRM, we had the option to use two service-level agreements (SLAs): Standard and Enhanced. But in Dynamics 365 CE, Standard SLAs are deprecated; we can only use Enhanced SLAs, which provide more flexibility, such as case-on-hold support, auto-pause and resume, and support for success actions.
• Relationship roles: Relationship roles have been around since Dynamics CRM 4.0, but now, these are deprecated from Dynamics 365 CE, and we need to start using connection roles instead.
• Mail Merge changes: The Mail Merge feature is also deprecated. Now, in Dynamics 365 CE, we need to use a server-side document generation feature, where we can generate Word and Excel documents using Word and Excel templates.
• Announcement changes: Announcements were used to share information with other Dynamics CRM users, but they are also deprecated.
• Legacy attribute for business process flow: In earlier versions of Dynamics CRM, when business process flow was enabled for the entities, it automatically added some fields to the entities, such as processed, stageid, and traversedpath, which are deprecated. Now, in Dynamics 365 CE, we have a separate entity for business process flow.

We need to check customers' customizations for the deprecated customizations mentioned in the preceding list, and we need to plan accordingly using the new features of Dynamics 365 CE.