Managing Mailbox Quota

Important Note:

Please click on the images to enlarge them

Managing mailbox quotas

Each organisation can permit up to 10% of their Exchange Online users to increase their allocated mailbox size from 4GB to 50GB, at no additional cost. The managing your organisation’s 10% quota section below details how LAs can allocate 50GB mailboxes to users.

The 10% quota is determined against organisation ODS code and is calculated based on the number of users in Exchange Online. The quota is recalculated daily, so if more users get licensed through the day, they would not be included in the quota calculation until the next day. If the full 10 % was initially allocated for an organisation, and the number of users then drops, the users will keep the larger mailboxes and the organisation won’t be able to assign anymore.

If you require additional large mailboxes in excess of your 10% quota, you will need to procure O365 licences (outside of the nationally provided license) and onboard them to the NHSmail central tenant. Please follow the onboarding for Local Administrators guidance in order to do so.

Please note:

all shared and resource mailboxes will receive a 50GB allocation as standard, and shared mailboxes cannot be reduced to 4GB.

Managing mailbox quotas through the NHSmail portal

Mailbox size management varies based on whether you are managing the 10% quota made available through the national dea l, or if your organisation has procured O365 licenses directly.

Managing your Organisation’s 10% quota:

Should you wish to increase a user’s mailbox to 50GB, please follow the below steps:

1. On the NHSmail Portal go to the User Details page via the Admin section.

2. Click on Edit Subscriptions within the Service Properties section.


Useful Information

  • If you are not able to click on the Edit Subscriptions button, you may not have the right permissions to manage mailbox sizes. You must have both the LA and Authorisation role to manage mailbox sizes.  Currently only LAs with the Authorisation role can manage mailbox size for users, both on premise and in Exchange Online.
  • If you are an LA allocating a larger mailbox on behalf of another organisation you need to ensure that you have the Authorisation role for that organisation. Please see information on how to add an Authorisation role. 

  • You can view the number of larger mailboxes set for the organisation in the Organisation Export Report under the Organisations tab. Please see the screenshot below for more information.


  1. On the Mailbox size, select the desired mailbox size and confirm.

1. If your organisation is a Digital Healthcare Frontline Worker organisation and the user is within your 10% quota allocation, the user will be assigned the larger mailbox once confirmed. It may take a small amount of time before this becomes visible to the user.

2. If the user’s organisation has reached the quota for larger mailboxes, you will not be able to assign a larger mailbox to the user. The number of assigned large mailboxes will need to be reduced to below the quota before a large mailbox can be assigned.


Managing quotas for directly procured O365 licenses:

Quota management for licenses procured directly by an organisation is handled through user policies in the NHSmail Portal.

Once you have onboarded your license subscription, please follow the below steps to configure a user policy with large mailboxes enabled.

  1. On the NHSmail Portal go to the User Policy Management page via the Admin section.
  2. When configuring a locally procured license, select the correct subscription from the drop-down menu – for example E1, E3 or E5.
  3. A Local Administrator (LA) has the option to provision a larger mailbox by toggling the Large Mailbox Size Enabled option to On.

4. All users within the policy will then be given the standard mailbox size attributed to the O365 license type, as shown in the table below.



Office 365 E1 50GB
Office 365 E3 100GB
Office 365 E5 100GB
Microsoft 365 E5 100GB
Important Note

Configuring large mailbox policies is only possible for users that reside in Exchange Online. Adding on-premise users to a policy with the large mailbox toggle enabled will not take effect, their current on-premise mailbox quota will remain as-is.

Granting Authorisation role

To add an authorisation role to a Primary Local Administrator or Local Administrator account please visit Adding Administration roles on how to assign a role.

Last Reviewed Date 1/12/2023
Updated on 01/12/2023

Related Articles

Need Support?
Can’t find the answer you’re looking for? Don’t worry we’re here to help!
Contact Support
back to top