Cached Exchange Mode with Extremely Large Mailboxes

Applies to: Cached Exchange mode with Mailboxes 18gb in size and over.

Outlook 2007 client hard codes max OST and PST size to 18gb warn and 20gb max for Unicode PSTs, and 1.8gb warn and 2.0gb max for ANSI PSTs. Once in warning mode, mail cannot be sent or received.

Solution:
On client machine where Outlook 2007 is installed.
Launch Regedit.
Navigate to the following key: HKCU\Software\Microsoft\Office\12.0\Outlook\PST (even for OSTs)
Create the key if necessary.
Create the following 4 DWords and populate them with the accompanying values:
• MaxFileSize=0x7bb04400
• WarnFileSize=0x74404400
• MaxLargeFileSize=0x0000c800
• WarnLargeFileSize=0x0000be00
Navigate to the following key: HKCU\Software\Policies\Microsoft\Office\12.0\Outlook\PST
Create the key if necessary.
Create the following 4 DWords and populate them with the accompanying values:
• MaxFileSize=0x7bb04400
• WarnFileSize=0x74404400
• MaxLargeFileSize=0x0000c800
• WarnLargeFileSize=0x0000be00

Restart outlook. Verify that mail can be sent and received.