How to Configure Quota limits from the Exchange Management Shell (EMS)
Set-Mailbox -Identity user@domain.com -IssueWarningQuota 4244635648 -ProhibitSendQuota 5242880000 -ProhibitSendReceiveQuota 5242880000 -UseDatabaseQuotaDefaults $false
Tip: When using the Exchange Management Shell the values are in bytes. To convert a megabyte value into bytes, simply multiply it by 1048576
For example, 5000 MB x 1048576 = 5242880000 bytes