Here we go again.
It appears that Microsoft going to actively block connectivity for older versions of Outlook on November 1, 2021 -- less than 11 months from now.
Previously, Outlook connectivity has always been best effort for older versions, meaning that if you can connect to Microsoft 365 with an older non-supported version, then great. If you can't connect, you are required to install a supported version.
The reasoning for this is noble - Microsoft doesn't want older less secure versions of Outlook to connect to the service. Most Office 365/Microsoft 365 customers are already running Microsoft 365 Apps for enterprise (aka Office ProPlus) which is always up-to-date, so no problem.
But future Microsoft 365 and hybrid customers will need to upgrade all their clients prior to migration, and a lot of enterprises won’t be able to update in that time.
The bottom line is, if your clients are not already running Microsoft 365 Apps for enterprise and you plan to migrate to Microsoft 365, you need to start upgrading your Office apps now.
Here is the notification from Microsoft:
Update to Microsoft 365 and Outlook for Windows connectivity
Major update: Announcement started
Applied To: All
To ensure that we meet performance expectations, we are updating the supported versions of Outlook for Windows that can connect to Microsoft 365 services.
Effective November 1, 2021, the following versions of Outlook for Windows, as part of Office and Microsoft 365 Apps, will not be able to connect with Office 365 and Microsoft 365 services.
Office and Microsoft 365 Apps
Outlook for Windows Version
15.0.4970.9999 and older
16.0.4599.9999 and older
Microsoft 365 Apps for enterprise (formerly Office 365 ProPlus)
1705 and older
Microsoft 365 Apps for business (formerly Office 365 Business)
1705 and older
- Major: Retirement
- Timing: November 1, 2021
- Action: Ensure Outlook for Windows client are updated accordingly
[How this will affect your organization:]
Versions that are newer than minimum version requirements listed above, but are not the currently supported version, may experience connectivity issues.
To see a list of the currently supported versions, visit Update history for Microsoft 365 Apps (listed by date)(for Microsoft 365 Apps) or Latest updates for versions of Office that use Windows Installer (MSI)(see “Latest Public Update” for Office 2013 and 2016).
Supported versions of Outlook for Windows in Office and Microsoft365 will continue to connect to Microsoft 365 services as expected.
[What you need to do to prepare:]
We recommend that all users upgrade to the supported versions of Office and Microsoft 365 Apps.