Hi @RemcoJ ,
Could this issue be reproduced on all Outlook 2016 client? What's the version of your Outlook 2016(File>Office account>About Outlook), please ensure that you have updated to the latest version of Outlook.
But when a user has a archive coupled it cant be searched
How did you add this archive folder(via adding a .pst file)? And did you test on Outlook 2013 with the same file? If not, it's suggested to use the same file for testing, if the issue could be reproduced on Other Outlook client, it may be related to your file itself, and it's suggested to repair your data file via scanpst.exe tool to check if the issue has any difference.
If the issue only occurred on this specific client, it's recommended to first check your Windows Index (File>Options>Search>Indexing options>Advanced>File types>check if the .pst type is checked). After that, if the issue still exists, we could try to troubleshoot the search and indexing or rebuild the search Index to test if the issue has any difference(File>Options>Search>Indexing options)
If that's not your case or you still need further assistance, please feel free to post back.
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