If you use Outlook with internet mailbox or with Exchange cached mode, outlook will use .pst or .ost file to store data.
Each of this files has his own maximum data limit supported by Outlook.
If this limit is reached .pst or .ost files are permitted to add any more data.
If outlook pst, ost file reach the size limit then you will get the warning.
Below, in table you can check maximum size limit, depended on Outlook version.
Outlook 2010
| Name | Type | Valid Data Range | Default |
| MaxLargeFileSize | REG_DWORD | 0x00000001 – 0x0000C800 | 0x0000C800 51,200 (50 GB) |
| WarnLargeFileSize | REG_DWORD | 0x00000000 – 0x0000BE00 | 0x0000BE00 48,640 (47.5 GB) |
| MaxFileSize | REG_DWORD | 0x001F4400 – 0x7C004400 | 0x7BB04400 2,075,149,312 (1.933 GB) |
| WarnFileSize | REG_DWORD | 0x00042400 – 0x7C004400 | 0x74404400 1,950,368,768 (1.816 GB) |
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