However, in Microsoft Outlook Web App (OWA), you don't see this warning. Instead, OWA displays a MailTip from the current forest.
For example, if the address is associated with a distribution group or a mail user, you receive the following error message in the Outlook logs:
MailTips from the current forest are displayed in OWA.
Article ID: 3083843 - Last Review: 04 Aug 2015 - Revision: 1