If your organization is already running an Exchange Server version, you should verify requirements for coexistence with Exchange server 2019 while planning your upgrade to exchange server 2019.
The supported coexistence scenarios between Exchange 2019 and its predecessor’s described in table below.
| Exchange version | Exchange 2019 Organization coexistence |
| Exchange 2010 and earlier versions | Not supported |
| Exchange 2013 | Supported with Exchange 2013 Cumulative Update 21 (CU21) or later |
| Exchange 2016 | Supported with Exchange 2016 CU11 or later |
| Mixed Exchange 2013 and Exchange 2016 organization | Supported if all Exchange 2013 and Exchange 2016 servers in the organization meet the requirements as mentioned above. |
Supported clients for Exchange Server 2019 include:
- Outlook 2019
- Outlook 2016
- Outlook 2016 for Mac
- Outlook 2013
- Outlook for Mac for Office 365