Hi Lincoln,
Thanks for you post.
The default configuration of Quota is not suitable according to your need. You can change the default mailbox size and configure it according to your need.
You just have to follow some steps to configure mailbox size according to your need.
First Go to Exchange Management Console then at left side of tree Select Organization Configuration and expand it. Now click on Mailbox and then Database Management. Now right click on database and select properties of Database and then click on Limit tab and define the limit what ever you want for your mailbox and click OK to apply.
I think this will help you.