Information
You can configure this setting to prevent users from sending new e-mail messages after their mailboxes reach a specified limit. To specify this limit, select the check box for this capability, and then type the size of the mailbox in kilobytes (KB) at which you want to prohibit the sending and receiving of e-mail messages and notify the user. You can enter a value between 0 and 2,147,483,647 KB (2.1 terabytes).
Rationale:
This setting prevents users from sending messages when their mailbox is approaching its size limit. However, they can continue to receive messages.
Solution
To implement the recommended state, execute the following PowerShell cmdlet:
Set-MailboxDatabase 'EXCHANGE01\Mailbox Database' -ProhibitSendQuota 2097152KB