Set a local mailbox size with the registry for GSSMO

When you use G Suite Sync for Microsoft® Outlook® (GSSMO), your mail is stored both remotely in the cloud, and locally in a mailbox (PST) file on your computer. The cloud can hold up to 30 GB of mail (or more), which is a lot more than you'd typically want to keep on your computer. The amount of mail stored locally is instead limited by Microsoft® Outlook's mailbox size.

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G Suite administrator can set the GSSMO mailbox size limit using a Windows registry key. For details, see Configure options and limits via the registry. Note that you can use either the registry key or the Set mailbox size limit command, but not both.

Refer below steps to set a local mailbox size by setting a registry key

By adding the following registry key and accompanying DWORD Value, you can limit the size of a user’s mailbox to a specific number of megabytes. This value also includes the size of delegated mailboxes that can be accessed. When you implement this registry key, the Mailbox Size Limit options are not available.

Create the following registry key and accompanying DWORD Value on each computer where Google Apps Sync is installed:

Add the following registry key: HKEY_CURRENT_USER\Software\Google\Google Apps Sync\EmailSync
Modify HKEY_CURRENT_USER\Software\Google\Google Apps Sync\EmailSync by adding the following DWORD Value:
DWORD Value name: MaxStorePstSizeMegaBytes
DWORD Value data: Enter the number of megabytes that you want as the maximum size of the mailbox (for example, 256 for 256MB)
The Outlook has some default PST capacity as Outlook 2003 and 2007 can go up to 20GB and Outlook 2010, 2013 and 2016 can go up to 50GB.
To define more than the default size of the Outlook PST capacity you must update the PST capacity first mentioned in this help guide.
Once you have updated the PST capacity you can define the local mailbox size accordingly.