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Outlook Guidelines

Outlook is a very powerful email client which can facilitate our office work enormously, provided a few "best practices" are followed. In fact, keep in mind that, while Outlook 2016 is installed locally on EUI's office desktop PCS, the Institute's email is stored in the cloud. In order not to incur in any syncing-related issue, the following guidelines should be put in place when managing your mailbox.

ICT Service cannot provide support with regards to the management of the contents of your mailbox however you should abid by the requirements of the EUI Records and Management Service of the HAEU and/or seek its support if your Unit does not implement any filing plan yet.
Please Note: failing to follow the below guidelines the ICT Service will not be able to guarantee optimal performance nor provide any support in case of Outlook failure!
  1. Maximum Amount of Items
  2. Maximum Amount of Items in System Folders
  3. Maximum Amount of Folders
  4. Cached Exchange Mode
  5. PST Files
  6. Maximum Amount of Additional Mailboxes






Maximum Amount of Items

Keep the total number of items (email, calendar invitations, etc.) in each folder below 100,000.


  • Create additional sub-folders in your Inbox, or directly in the "root" of your mailbox, where to move and store your email (however please make sure to reamin within the maximum number of allowed folders).


Maximum Amount of Items in System Folders

Additionally, for the so-called Outlook system folders, keep the number of items (mail, calendar invitations, etc.) in the Inbox, Sent Items, Drafts and Deleted Items below 10,000 each.


  • Create additional folders in your Inbox, or directly in the "root" of your mailbox, and split the content of the larger ones in the new and/or smaller folders (however please make sure to reamin within the maximum number of allowed folders).
  • Avoid putting yourself in CC/BCC when sending email. A copy of any outgoing email is already available in the Sent Items. If you want the email you sent on behalf to be available in the Sent Items of a mailbox you are delegate of (rather than in your personal one), contact the EUI Helpdesk.


Maximum Amount of Folders

Keep the number of folders in your Outlook below 500 folders in total.



Cached Exchange Mode

In order to avoid performance drop while syncing email in the cloud, Outlook can download a local copy of your email and store it on your PC. When this option is active, Outlook will work in so-called Cached Mode and moving among mail and mailboxes, as well as Search results, will be faster.

For best performance, Microsoft suggests to keep a copy of not longer than one year and Institute's PCs are setup accordingly by default. Additionally, in order to avoid excessive data usage, any shared mailbox is setup as not to cache its content.


  • Do not change these settings in order not to incur in slowdowns (particularly when moving from one mailbox to another one) or bad performace/low results while Searching your mailbox.


PST Files

PST files are local archive folders of your email which should be avoided at any rate as they can significantly slow down your Outlook or, worse case, get corrupted with a result of loss of your email.


  • Create PST files for the only purpose to create one-time achives: PST files should in no case be running archives, i.e. where you add mail day by day.
  • Open PST files only when in need of retrieving email, do not use it for frequent reviewing of your archived email.
  • Do not open PST files directly from a network share as you may experience huge performance drops: if you need to open a PST in order to look for an archived email, it is suggested to keep the original PST archive on the network share (for backup purpose) and temporarily create a local copy of it instead (which you should delete afterwards).


Maximum Amount of Shared Mailboxes

If you are working in a team or have an instituional role, you most probably will use one or more additonal shared and/or "service" (impersonal) mailboxes (of which you may be as well Delegate of).

Microsoft indicates the maximum number of additional mailboxes should not exceed 10: if you have more, it is very likely you may incur in performance loss.


  • Reduce the number of additional mailboxes
  • Explore the possibility in some of the service mailboxes to automatically distribute incoming mail to your personal email account instead, as this will reduce the amount of mailboxes you may want to see, and check, within Outlook.



Page last updated on 01 October 2018

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