OLM file came into existence with the introduction of Outlook 2011 for Mac. OLM files are the master repository file format of Outlook for Mac for storing local data (such as emails, attachments, contacts, calendar data, tasks, notes, journal etc.) of outlook.
OLM file is not created by default; it can be generated via different export methods. Moreover you can filter the information depending on the type of data that is required to reside in the file. The Maximum size of OLM file is not specified anywhere but generally OLM file doesn’t exceed 2GB in order to minimize the Corruption issue.
How to Open & View OLM file?
OLM file are only used by Mac Outlook and can't be accessed or opened by Windows version of Outlook. As the Windows version uses only .PST file format for mailbox data. To open OLM file in Windows, you need to convert OLM file to PST file format.