With the huge size of mailboxes possible in Exchange Online and Exchange on-premises, the size limit of OST files is a problem.
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Today, Outlook will use the Unicode file format by default. The older ANSI format has an OST file size limit of only 2GB. The limits above apply to OST files in Unicode format, also known as “Large format”. Outlook 2010 is also out of mainstream support, so hopefully if you are still running Outlook 2010 you are planning an upgrade in the near future. Hopefully you’re not running Outlook 2007 or 2003, both of which are unsupported today. Outlook 20 and earlier support an OST file size of up to twenty gigabytes (20GB).
![cached exchange mode outlook 2010 greyed out cached exchange mode outlook 2010 greyed out](https://www.nucleustechnologies.com/blog/wp-content/uploads/2018/04/162.-What-is-Cached-Exchange-Mode-in-Outlook-_odt_mfb4026f.gif)
![cached exchange mode outlook 2010 greyed out cached exchange mode outlook 2010 greyed out](https://www.technipages.com/wp-content/uploads/2011/09/Outlook-2010-Trust-Center-Settings-button.png)
Outlook performance in “on-line mode” is not all that great. When you connect Outlook to an Exchange account, Outlook downloads a copy of your mailbox content to a local cache.
CACHED EXCHANGE MODE OUTLOOK 2010 GREYED OUT HOW TO