First, check that the message...
If all the above are true, this is almost certainly a genuine message sent from the University's Exchange mail system, and applies only to staff and research students.
When your mailbox is approaching capacity, Exchange will send you a warning email (labelled as being from Microsoft Outlook) showing you how much space you are using and how much is left. However, it is for information only and does not ask you to reply or to disclose any information in any way, so can be considered safe. Outlook Web App (OWA) will also show an on-screen warning when you login.
Any other email about your email quota is almost certainly a fake and must be ignored - see our important article about phishing emails.
If you do nothing, you may soon find that you are no longer able to send email, and later still you will not be able to receive any email either. Outlook will also show an on-screen warning when you reach this stage, so as to act as a constant reminder.
The warning messages and emails are explained in more detail (with illustrations) in FAQ 2350, which also tells you more about the Exchange mailbox quota mechanism.
For details about emails which should not be trusted, please read FAQ 1446.
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