Open PowerShell on the Exchange Server and use this script:
Displays an early warning to notify users that they are approaching their limit:
-IssueWarningQuota 10gb
After the mailbox reaches this limit, you are not allowed to send mails anymore:
-ProhibitSendQuota 11gb
This is your hard limit. After reaching this, you are not able to receive any mails:
-ProhibitSendReceiveQuota 12gb
To actually use this quota, you will have to “ignore” the database default:
-UseDatabaseQuotaDefaults $false
