Common email issues on managed staff desktops

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The more mailboxes you have open, the more data there is to synchronise. This will degrade performance of the Outlook app.


Keeping mailboxes open will affect performance of Outlook. Only open mailboxes when you need to, and close the mailbox when you have finished. For further guidance, please see our Nexus support pages.

To close a mailbox

  • You can close unused mailboxes by right-clicking the mailbox and clicking Close [mailbox name] from the menu.
  • If you do not see the option to close, please contact the Service Desk, asking to turn off auto-mapping on that mailbox. When auto-mapping has been turned off, the mailbox will disappear from your Outlook.

To add a mailbox

  1. Within Outlook, click on the File menu and the on the Account Settings button

  2. Select Account Settings from the drop-down list.

  3. Select the Email tab, click your account in the list, then click Change and then click More Settings.

  4. On the Advanced tab, under Open these additional mailboxes, click Add and enter the mailbox name that you wish to add to your profile.

You will need to configure Outlook to use Nexus the first time you login to a managed device. Our help page, Outlook on Nexus365, tells you how to do this.

Outlook is configured to run in Cached Exchange Mode on managed devices, and may become unresponsive when opening and closing the application.

If you open a mailbox that appears to be empty or incomplete, then check the bottom right-hand corner of Outlook because there may be a message indicating that Outlook is still synchronizing with Nexus. The mailbox contents should display after a few minutes. Once finished, a copy of your mailboxes are on your device.

Locally cached mailboxes are stored in OST files, and the size of the files stored on your device, corresponds to the size of the mailboxes on Nexus.

About the size of OST files:

  • An OST of under 10GB, should not cause unresponsiveness on most modern devices
  • Outlook may become briefly unresponsive as the OST approaches 10GB
  • When the OST grows beyond 25GB, you may experience extended periods when Outlook is unresponsive
  • An OST cannot grow beyond 50GB.
  • RSS and Internet Calendar subscriptions may cause Outlook to become unresponsive.
  • We strongly recommend that you do not use PST files to archive your email.
    • PST files stored on your device are not backed up and may contravene data protection policy.
    • Using PST files on a cloud service or network location is not supported by Microsoft or The University.
    • Using PST files will degrade performance of Outlook.
  • Keep the size of your mailbox to a minimum, save attachments elsewhere, and remove old items.
  • Opening 500 or more folders, across all mailboxes, is known to cause inconsistency and poor performance with Outlook.
  • Open mailboxes when you need to use them, and close them when you are finished.
  • Don't set Outlook to automatically open when you login to a device.
  • Nexus Webmail provides quick and easy access to mailboxes, without having to configure Outlook or cache mailboxes on your device.

Having more than 500 folders may degrade performance in Outlook.

The 500 folders are counted across all the mailboxes you have opened, and that are stored on the same mailbox server, including your own mailbox.

This is a default limit when accessing mail with Outlook, and will cause caching problems and synchronisation errors for users that are above this limit.

For further information on this, please refer to the Nexus support pages. If you are over this limit of folders, you may receive an insufficient memory error when attempting to access folders, as per the Microsoft guidance here. (This article specifically references Public Folders, however the same applies to primary and additional mailboxes.)

Each open mailbox consumes resources  on your device. 


As your mailbox size increases, more resources are needed to open each folder. If you have a large number of items in any single folder, you are likely to experience performance issues. A significant amount of your mailbox quota is likely to be taken up by attachments. These can be stored elsewhere rather than in your mailbox.

If you have more than 50,000 items in a single folder, views other than Arrange By: Date can be slower. It is recommend by Microsoft that you move several items in these larger folders to separate folders in the same store or to an archive store and that you use Arrange By: Date when you run Outlook 2010. Please be mindful of the 500 folders limit when making any changes

With Nexus 365 via the Web, you can access your mailbox from any device with an internet connection

  • You can use any internet browser
  • You do not need to configure it for the first time
  • You can open other mailboxes via delegation
  • Your email is not stored on the device
  • Our help page, How to log in to Nexus365 via the Web, has more information

Outlook is part of the Managed Desktop Service, and supported by The Service Desk.

You can use an alternative email client, such Thunderbird, but please ensure that caches are not stored in your user profile, or compromise data security. 

Our guide, How to configure your email client, can help with manual configuration.

We recommend that all email is stored within Nexus, and that users do not export mail to PST archive files.

Outlook data and archive files, known as PST files, can easily become corrupt. These files are not stored within Nexus, and by default are stored on the local hard disk of the machine you configure them on. These files will not be backed up.

PST files should never be opened from a network location. This includes your home drive (H:\).

The use of PST files is also known to cause performance issues during certain operations in Outlook. This can cause the application to 'freeze' whilst it synchronizes the PST file, with issues especially noticeable when you switch into and out of folders that contain numerous items.

If you use Outlook to connect to other email accounts, such as POP3 or IMAP, Outlook will also store these email accounts to a local Outlook data file. We do not recommend that you use Outlook to connect to any other mail sources outside of Nexus.

Although you are able to start opening applications immediately after logging on when you see your desktop, there are still processes finishing in the background that aren’t visible to you. Waiting a few minutes after your desktop appears will allow those processes to complete and your computer will then be able to use all of its resources to open your application.

If you have chosen to run Outlook immediately after your computer starts (by placing these in the start-up folder) you should be aware that Outlook will be slower to start-up as there are other tasks completing in the background just after login.

Using RSS and Internet Calendar subscriptions is known to cause synchronisation issues, with symptoms such as Outlook running very slowly, not showing up-to-date calendar information, or reporting connection failures.

To check if you have any RSS Feeds

  1. Within Outlook, click on the File menu and the on the Account Settings button
  2. Select Account Settings from the drop-down list.
  3. In the Account Settings window, click the RSS Feeds tab.
  4. Any active RSS feeds you have will be listed. To remove any, highlight the feed name and click on Remove.

To disable RSS Feeds

  1. Within Outlook, click on File menu and then Options.
  2. In the Outlook Options window, click on Advanced.
  3. Scroll down to the RSS Feeds section and untick Synchronise RSS Feeds to the Common Feed List (CFL) in Windows.

To check if you have Internet Calendar Subscriptions

  1. Within Outlook, click on the File menu and the on the Account Settings button
  2. Select Account Settings from the drop-down list.
  3. In the Account Settings window, click the Internet Calendars tab.
  4. Any active Internet Calendars you have will be listed. To remove any, highlight the calendar name and click on Remove.

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