Hi @Tom Chudomelka ,
Thanks for visiting our forum.
Before going further, what does the "group addresses" you mentioned exactly mean? Do you mean Outlook contact group email address or something else?
As I know, simply upgrading the Outlook client version will not affect the data of your mailbox. In Outlook desktop client, we could find all our groups via Address book like below:
If this is not your case, in order to better solve your issue, please provide me with more information related to your issue, for example, screenshots of your issue. (Notice: Please hide your personal information in the screenshot for security.)
By the way, if you are using Exchange email accounts, it is suggested for you to check your "group addresses" via your web mail and see if the issue has any difference.
Any updates, please feel free to post back.
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