A 50 GB file is very very big and it might take a big time to load it. Typically, if the file is in a proper condition, Outlook will open it, only that it will take a very long time. I also wouldn't recommend using another application to mess with the file or you'll render it corrupted, because many of these so called file browsers and file fixers will just destroy the original data. Instead, use Outlook and wait for the whole file to load because 50 GB for email is huge and takes time. Once loaded, perform one single action at the time.