When you add shared calendars to your Outlook, you always try to add through Distribution List first and then individual ones if the Distribution List is just too big of a group. And that’s what I’ve been doing for a very long time. But recently, I am having trouble adding Distribution List as shared calendars in certain Outlooks. It always tells me to add each calendar individually.
Turns out, there is a shared calendar improvements feature added in recent Outlook releases. And it’s turned on by default on all new Office 365 installations.
To disable it, open Account Settings by going to Files, click the Account Settings button, and choose Account Settings.
Click the Change… button in Account Settings to open the Exchange Account Settings dialog box. Click the More Settings button at the bottom of the window and switch to the Advanced tab, where you will find the option “Turn on shared calendar improvement” under Microsoft 365 Features section. Make sure to uncheck it and click OK to save the change.
Once done, restart Outlook and try to add the shared calendars again.