Don't see this mentioned here, so thought it was be good for others. Users will no longer be able to search All Mailbox items or similar searching when messages have moved to this additional auxiliary mailbox. They MUST select the folder for where the message would have been stored to search. What is not mentioned is "Sent items" folder does not seem to working. This particular user which has 130GB in their Archive Mailbox(es), their sent items only go back to 2018 and cannot be used to search either. They however can find a corresponding message in another folder before that date. "You can search for items that were moved to an additional storage area only by searching the folder itself. This means that you have to select the archive folder in the folder list to select the Current Folder option as the search scope. Similarly, if a folder in an auto-expanded storage area contains subfolders, you have to search each subfolder separately."