Microsoft 365 Retention Policy shows "Exchange: 1 distribution result(s) found - Notify Support"

Microsoft 365 retention policies are configured from Policies in the Microsoft 365 Compliance Center (https://compliance.microsoft.com). You can create retention policies to keep and or delete data in Exchange email, SharePoint sites, OneDrive accounts, Office 365 Groups, Skype for Business, Exchange Public Folders, and Teams channel messages and chats.

When setting up a new retention policy it defaults to configure a policy for Exchange email, SharePoint sites, OneDrive accounts, and Office 365 Groups.

As of this writing, separate retention policies are required for Microsoft Teams data.

If you select Exchange Public Folders but you don't have them in Exchange Online, the policy will show an error saying, "1 distribution result(s) found". The Exchange location has the details, "Recipient not found" and the Action will say, "Notify support".

This isn't a very helpful error message. "Recipient not found" means that the policy couldn't locate the Public Folders mailbox. 

To fix this, simply edit the policy to not include Exchange Public Folders and save it. The policy status will change to "On (pending)" while the change is replicated through all the services. In a short while the status will change to "On (success)".