When the original account is down, you may still view or back up Outlook data by converting OST files to PST format. The most frequent way is to use Outlook's Import/Export function (File > Open & Export > Import/Export > Export to a file > PST). You may also use a third-party program like FixVare OST to PST Converter to easily convert OST files to PST format without any problems. It keeps the data safe, keeps the folder structure the same throughout the conversion, and saves the PST file for data protection.
More Information: https://www.fixvare.com/products/ost/pst/
More Information: https://www.fixvare.com/products/ost/pst/