As part of it, Outlook client older than the below version will not be able to connect to Office 365 services after November 1st, 2021
- Outlook 2013 15.0.4970.9999 and older
- Outlook 2016 16.0.4599.9999 and older
- Outlook ‘M 365 Apps’ (aka Office 365 Pro Plus) 1705 and older
If you are still running any of these version start planning your upgrade to avoid connectivity issues.