Using Classic Outlook on Windows for personal email, calendar, and contact management
I thought I had a solution with a Custom Search Folder, but even though you can search All Mailboxes from the search bar, when I tried to create a Custom Search Folder using Advanced Search, it wouldn't allow searching multiple IMAP accounts. Back to square one.
So I created a macro that performs the search instead and put it on the ribbon. Ugly but works.
Sub Inbox()
Dim myOlApp As New Outlook.Application
txtSearch = "folder:Inbox"
myOlApp.ActiveExplorer.Search txtSearch, olSearchScopeAllFolders
SendKeys "{TAB}"
Set myOlApp = Nothing
End Sub