Seeking Assistance: Outlook Warning, Storage, and OST File Limit

Hi Frank_Lee,

thanks for the update.

This issue is specifically related to Outlook 2010 and later versions, where the default maximum size for .ost files is set at 50GB, independent of your overall mailbox storage.

Despite having a 100GB mailbox, the .ost file has its own size limit, leading to the warning message you're seeing.

To manage this situation, consider the following options:

1. Clear Out the Mailbox: Regularly delete unnecessary emails and attachments, and empty the "Deleted Items" folder.
2. Adjust "Mail to Keep Offline" Settings: Reduce the amount of mail kept offline in the OST file.
   Work offline in Outlook - Microsoft Support
3. Move Mail Items to Archive Folder: Move older items to an Archive folder.
   Archive in Outlook for Windows - Microsoft Support

If needed, you can increase the .ost file limit beyond 50GB by adjusting registry entries.
https://support.microsoft.com/en-us/topic/how-to-configure-the-size-limit-for-both-pst-and-ost-files-in-outlook-2f13f558-d40e-9c2a-e3b6-02806fa535f4