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Questions and answers

Exchange mailbox quota - an introduction

Each member of the University has, as standard, a 2GB quota for email storage.  As you approach this limit you will receive a warning.  You can then either take steps to reduce the space currently used or request an extension to the storage limit using our online form.

You can also check how close you are to your storage limit at any time.

About the Exchange mail storage and quota system

  1. About the Exchange mail storage and quota system
  2. How (and when) Exchange tells you when you're short of mailbox space
  3. What to do if you run short of mailbox space
  4. How to find out how much mailbox space you're using

The University's email and calendaring service for staff and PhD students is hosted on a Microsoft Exchange 2010 system.

In Exchange, mailbox is the name given to your entire collection of email folders, including your Inbox.  We may sometimes refer to it as your mailstore.

Exchange uses a quota mechanism which determines how much email can be stored in your mailbox.  This is a limit on the amount of storage space you can use (usually measured in Gigabytes or GB), not the number of messages you can keep.  If you use Outlook or OWA for your email, this will include deleted messages and folders, which are stored in your Deleted Items folder but will continue to use storage space until you empty it.  When you empty the Deleted Items folder, this frees storage space in your mailbox and the items are moved to the Exchange dumpster (sometimes called the Recoverable Items folder) where they stay for 28 days just in case you needed to recover deleted items.  After the 28 days have elapsed, the items are removed from the dumpster and are no longer recoverable.

If you do not use Outlook or OWA, storage of deleted messages will be determined by the available options for the email application you are using.  Some applications do not store deleted items at all, but delete them from your mailbox immediately.  Other applications may use another folder such as Trash.  It's important to remember that if 'deleted' email is put into a Trash folder or similar, it will still consume the same amount of storage space until that folder is emptied, either partially or completely.

The Microsoft Exchange system notifies you by email if your mailbox usage is close to, or has exceeded, your quota limit, according to a series of thresholds.  The section How Exchange tells you... below shows an example of such a warning.

There are three levels of quota control thresholds:

  1. Your Warning threshold is the limit at which the Exchange system warns you that you are close to running out of space.   When this happens, you will be sent an email warning you that "Your mailbox is almost full".
    You can continue sending and receiving email, but you must take action (see below) to resolve the problem.

  2. Your Prohibit Send threshold is the limit at which the Exchange system will prevent you from sending email until you have done something to resolve the problem.  You'll receive an email saying "Your mailbox is full".
    You will still be able to receive email for the time being, but you must take immediate action (see below) to resolve the problem.

  3. Your Prohibit Receive threshold is the limit at which the Exchange system will prevent you from both sending and receiving email.  You'll receive an email saying "Your mailbox is full". If you reach this threshold then it is urgent and imperative that you immediately do something about it (see below).

Nominal mailbox quota thresholds for new accounts are:

2.15 GB for the Warning threshold

2.25 GB for the Prohibit Send threshold

2.56 GB for the Prohibit Receive threshold.

If you have recently been transferred to Exchange from the student mail system, these thresholds may be higher, depending on the amount of email you had when your account was transferred.  Your mail quota on Exchange will have been matched to, or set slightly higher than, that on the student mail system.

How (and when) Exchange tells you when you're short of mailbox space

There are two ways in which you are told when your mailbox space is running short or has been exhausted:

1. Emailed warnings

When your mailbox reaches its Warning threshold, Exchange will send you an email (apparently from 'Microsoft Outlook'), not immediately but at around 2am each day, showing you how much space you are using and how much is left before your mailbox reaches its Prohibit Send threshold.  An example is shown below.  As can be seen, the message contains no clickable links, no attachments, and does not ask you to reply in any way with any information.  Any similar message which asks you to reply, or click a link, or open an attachment, is fraudulent and must be ignored. You can verify your mailbox space usage by following the instructions below, under the heading How to find out how much mailbox space you're using.

As seen in Outlook or Outlook Web App (OWA), the message will look something like this:

Quota warning threshold message

The plain text version, as may be seen if you view emails as plain text in Outlook, will look something like this:

Quota warning threshold message (plain text)

Don't these warning emails take up even more mailbox space?

No. The nightly warning emails are system-generated emails, and as such do not count against your personal mailbox quota, and so will always be delivered no matter how full your mailbox is.  This helps to maintain your awareness of the problem.

2. On-screen warnings

When you login to Outlook or Outlook Web App, a warning note is shown near the top left of the application window.

Outlook shows the following warning only when your mailbox has reached its Prohibit-Send or Prohibit-Receive threshold:

Outlook 2010 quota warning

Note that Outlook does not show an on-screen warning when your mailbox has only reached its Warning threshold, but you would get an emailed warning (see below).

Outlook Web App (OWA) is more informative, and shows a message similar to that shown below when your mailbox reaches its Warning threshold:

OWA: mailbox storage quota warning

When your mailbox is full (that is, it has reached your Prohibit-Send or Prohibit-Receive thresholds), OWA will show the following warning:

OWA: mailbox storage quota final warning

Note that the examples above are from a test account with a very low quota setting, hence the tiny threshold values!

What to do if you run short of mailbox space

Delete stuff!
The first and most obvious thing to do is to delete as much old and unwanted email from your Inbox and from as many other folders as possible.  Be ruthless!  You really don't need to keep everything.  Get into the habit of doing this regularly, then you are less likely to run into problems with lack of mailbox space.  Don't forget that you'll also need to empty your Deleted Items folder (see below).

Consider adopting the practices recommended by the Email Charter so as to cut down on unnecessary email.

The University of Brighton's Information Services, who have operated an Exchange mail system for many years, have a very useful and forthright article titled "How not to drown in email".  You will find that almost all the information given there is equally applicable to your use of the Sussex Exchange system.

Empty your Deleted Items folder
Remember that if you use Outlook or OWA, when you delete items they do not disappear immediately.  Instead, they are moved to your Deleted Items folder and continue to use the same amount of mailbox space.  You need to empty or at least drastically reduce the number of items in your Deleted Items folder, which can rapidly accumulate a great many messages.  If you aren't using Outlook or OWA, check to see if your email application uses another folder to store deleted email (such as Trash).  If you don't want to completely empty the folder, consider deleting messages in it that are older than a certain age, for example two or three months.  It's easy to do this by block-selection of messages, as described in FAQ 2487.

It's also a good idea to do the same thing with your Sent Items folder, which Outlook and OWA use as standard to store copies of all the email you send.   It's unlikely that you need to keep all this, especially emails sent longer ago, so it's worth getting into the habit of removing as much old email as possible from Sent Items.   Remember though that the items you delete will be put into the Deleted Items folder (see above)...

Store files separately, not in your email
Email attachments are usually the cause of the greatest use of mailbox space rather than sheer quantity of messages.  Attachments are stored very inefficiently, and typically consume far more storage space than the original files.  Nor can attachments be changed.  Consider saving attachments to their own files, and deleting the attachments from the messages.  This is easy to do in Outlook, and is described in FAQ 1532.

Consider also making archives of your email.   This is discussed in FAQ 1456 Please note that if you choose to make an archive on an external medium or on your computer's own hard drive, neither of which benefit from IT Services backup procedures, you must take responsibility for the safe keeping of those archives.

Ask for more email storage space
If, despite all your efforts to reclaim mailbox space you are still short, you can request an increase.   Please go to the IT Support page, then click the increase file space or mail quota icon, then complete the form that appears, being careful to select the mail increase option.

IT Services do not encourage the use of email for storing business related information or academic data as the system is not designed for that purpose and if you have a large folder structure and your account is compromised although we can restore emails we may not be able to restore the folder structure .

We recommend that you use manual archiving for email folders as described in this FAQ - . This has the advantage that the files are stored on our file servers which are easier to restore from if an issue should arise and also improves the performance of the email system.

Don't leave it too late before requesting an increase.  Many people seem to wait until they reach their prohibit send threshold, and suddenly find themselves unable to send any email.

How to find out how much mailbox space you're using

OUTLOOK (version 2013 and 2016)

  1. Click on the File menu tab.   In the Info section you will see a Cleanup Tools button, alongside which is a measurement of how much mailbox space you have free, and the total amount of mailbox space available, measured in GB (Gigabytes). In the example below, a total of 2.34 GB is available, and 2.02 is free, so 0.32 GB is being used.

    Outlook 2010: mailbox size


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Created by Andy Clews on 18 July 2011 and last updated by Gemma Sturtridge on 25 March 2020