Split an oversized OST file into multiple PST files
An Outlook OST file contains all the mailbox data since the time an email account was created. These may include contacts, calendar entries, tasks, journals, emails, files and so on. Large OST files can be difficult to manage and can cause performance issues in MS Outlook. This is because Outlook has a limit on the size of data files and may crash if the file size exceeds the limit. To avoid this problem, it is best to split large OST files into multiple PST files when exporting or backing up your emails to PST.