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OLM aka Outlook For Mac files are the proprietary file format of Microsoft Outlook For Mac. Outlook for Mac as suggested by the name is supported in Macintosh operating system and is analogous to MS Outlook that is supported in Windows operating system. A single OLM file stores the entire Mac Outlook data comprising of emails, contacts, calendars, etc.
Originally, OLM files came into existence with the introduction of Microsoft Outlook 2011 for Mac in the year 2011. Although the OLM files are the master repository for storing local data of Outlook for Mac but it is not created by default. The OLM files can be generated via different export methods. While exporting data to an OLM file, the information can be filtered out depending on the type of data that is required to reside in the file. In case there is a need to export only Networking information to an OLM file, the items that have been assigned to the Network category should be exported in the OLM file. To prevent exceeding the maximum size limit, the emails in the Outlook for Mac can be archived in an OLM file.
OLM files were first introduced with Microsoft. The maximum size of the OLM files is not specified but in general the size should not exceed above 2 GB. Exceeding the 2 GB size may lead to failure in exporting the OLM file if needed.
No corroboration so far has been released for supporting Outlook Mac OLM files in Windows or any other non-Macintosh machines. Although third party implementations have successfully achieved this success in accessing OLM files in Windows machine.