To split a massive 100GB PST file without crashing Outlook, using a specialized tool like DataVare Outlook PST Split Expert is the safest approach. Make sure Outlook is completely closed and that the PST is not configured as the default destination place. If you try to view huge files directly they can slow down or crash Outlook. Open the program upload the large PST file, and then pick a way to split it up that works best for you such as by size, date or folder. Choose the option to keep the folder structure so that no emails or subfolders are lost. Set a sensible size limit for each smaller PST so that Outlook stays steady when you access them. The tool makes several smaller PST files that keep the original structure after the procedure is done. You can then open these in Outlook without any problems or crashes. This method does not need dividing by manually, which can be problematic and lead to mistakes with really large PST files.