A user can't open encrypted emails on the computer but can on the old one

@Jean Olivier Gasore , if you try using Set-AIPFileLabel, do you see any additional messages in the error logs? Note that when document has been signed through a digital signing provider, the error you cited is expected since AIP cannot protect a file that has been previously encrypted or locked.

Does this also also affect or can be a reason why encrypted emails with current version of Desktop Outlook cannot be opened or read in Desktop outlook?; -where the view msg button in body of email opens in the web browser to view it, but says the "message has moved or has been deleted">?