I have this very weird issue with a customers migrated mailboxes. They have been moved from Notes to 365 recently and confusion is ruling the place at the moment.
I have been asked to look at weird problem where Outlooks "Search People" returns a non-existing onmicrosoft.com address and also when typing the emailaddress in the To field in a new email Outlook automatically suggests this same address (among others). When choosing the address in the new email Outlook tries to resolve it to a recipient but fails and just show the display name. (see attached pictures)
And no, there is no X beside the address that makes it possible to delete it.........if only ;)
I hav tried emptying the autocomplete list but this dosn't change anything and I have searched high and low for the address in the tenant and the addressbooks availabl to me in azure and exchange online. I have spend a lot of time troubleshooting now. For example I have: located some send emails in the users send folder with the address in the to field and removed them, created a new outlook profile, changed to online mode, cleared search index and afterwards removed all indexing locations but still the address pops up when I either start typing it in a new email or in the "Seach People" field. When I start typing the emailaddress through Outlook online (owa) the address doesn't show up so I belive that it has something to do with the mailbox content and/or Outlook functionality.
This is not the only user who has this problem and it is not the only non-existing address that haunts the place, several people have the same issue with this address and other addresses.
I can't rule out that the address once existed in either Notes for migration reasons or in O365, and then got deleted afterwards.
So I'm hoping that someone can shed some light on this issue. For example when using the Search People, where does Outlook search? How come OWA doesn't show the address but Outlook does in both cached and non-cached mode? Can there exist some addresslist in another 365 application that Outlook searches in and find these non-existing addresses?
I'm testing on a totally different computer where I just logged on as one of the users who is experiencing the problem, and configured outlook and probably also other MS applications with the users O365 credentials, so it is not just in the users current profile that the issue exists, it is reproducible on other computers.