The limits of Shared Mailboxes in Office 365



I get lots of questions about the Shared Mailbox in Office 365, especially on how it works with the licensing.

Does a common shared department mailbox take an Office 365 license ?

Shared Mailboxes in Office 365 (Exchange Online), allow a group of users to view and send e-mail from a common mailbox.

I will try to describe the details in this blog post.

Shared Mailboxes in Office 365 and licensing

With Office 365 (Exchange Online) it is possible to create Shared Mailbox for common services (e.g. department mailbox with a generic mail address such e.g.

A Shared Mailbox is free and requires no Office 365 license.

The limits

There are however a limit to using Shared Mailbox, if you want to stay within the free license. Not many are aware of this, but a Shared Mailbox cannot grow larger than 5GB, if it exceeds the 5GB limits it needs an license!

Set quota on your Shared Mailboxes

The best way to setup your Shared Mailboxes, are with a Quota, this way you know, they will not exceed the 5GB limit.

Here is how to setup the quota for a Shared Mailbox:

Set-Mailbox SharedMailboxName -ProhibitSendReceiveQuota 5GB -ProhibitSendQuota 4.75GB -IssueWarningQuota 4.5GB

If you want to set the quota on all your Shared Mailbox with one command, you can use this powershell command:

Get-Mailbox -ResultSize Unlimited -filter {RecipientTypeDetails -eq “SharedMailbox”} | Set-Mailbox -ProhibitSendReceiveQuota 5GB -ProhibitSendQuota 4.75GB -IssueWarningQuota 4.5GB

See my previous blog post on how to connect to your Office 365 tenant using Powershell: How to Remote PowerShell into Exchange Online (Office 365).


To sum up on the details of a Shared Mailbox:

  • A Shared Mailbox do not require a license, but every user that accesses the Shared Mailbox must be assigned a Office 365 license
  • A Shared Mailbox cannot be accessed by users with Exchange Online Kiosk license
  • A Shared Mailbox has a maximum size of 5 GB. Exceeding this limit will require as a minimum an Exchange Online license
  • A Shared Mailbox can be used to store e-mails sent to and received by the Shared Mailbox
  • A Shared Mailbox can be used to store data migrated from on-premises Public Folders
  • A Shared Mailbox cannot be used to archive e-mails for individual users

In Office 365 and Exchange Online, Shared Mailboxes can only be created using Remote PowerShell. See my blog post: How to Create a Shared Mailbox in Office 365

41 thoughts on “The limits of Shared Mailboxes in Office 365”

    • Thanks for the update.
      This info I posted was for the “old” Office 365. The New Office 365 has been updated with other limits. Listed in the technet article, as you referred to.

  1. IMHO, the biggest limitation here is the lack of support for accessing a shared mailbox from a mobile device like Windows Phone 8.

  2. Is it possible to have emails that are sent to a shared mailbox of which I am a member, go to a subfolder of my main inbox? I am a member of some infrequently used shared mailboxes and I don’t always spot new emails.

  3. Hi Peter,

    Good article, i have one question about a shared mailbox and that’s does this mailbox also include a shared calendar, or is it purely a shared inbox?


    • If you have setup mail flow between your environment, you should be able to send between on-premise and online.
      Are you running Hybrid ?

  4. What are the consequences of attempting to use a Shared Mailbox to archive individual user emails. I ask because we had this very idea as a simple method to make project related email available to all users. Our plan was to physically move the emails to this mailbox, not copy. In a dry test, functionally this worked. Is there a licensing issue here? Your statement “◾A Shared Mailbox cannot be used to archive e-mails for individual users” is false in regards to functionality from what we’ve been able to tell. We have not actually started doing this. Just tested it. Let me know your thoughts. Thanks

  5. Hi Peter,

    How can be configured a shared mailbox in order to have its shared calendar be read-only for some users? The objective is to have read-write for some users and read-only for other users.


  6. What uses less bandwidth. Sending an email to a shared mailbox with 10 people or that same mail to 10 individual mailboxes. All in Office 365. Thanks

  7. Hi Peter,

    We’re running into an issue where if a user has multiple Shared Mailboxes, it combines them with their own mailbox and then it hits the 50GB limit. I’ve done the regedit hack to stop this, but is there a way to stop it from coming up for other users in the future?



    • Hi Tom
      I have not seen that. Those multiple shared mailboxes are created a Shared Mailboxes and then permissions is assigned to certain users ?


  8. Is there a limit on however users I can assign full access permission on a shared mailbox?

  9. Is there a limit on how many users I can assign full access permission on a shared mailbox?

  10. Hi there,

    Our share mailbox has 4.7 GB space and now we just found out that its exceed the limit and now its 8GB used from 4.7 GB, I know we can increase the size anytime but wondering what happens if a share mail box exceed the limit before we increase the size ?


  11. Great article Peter, Many thanks.
    I do have a question for you:
    Is there a way to prevent deletion of items from a shared mailbox in O365?

  12. Hello,

    Shared Mailboxes are free, but what is the maximum number of shared mailboxes that can be added to a Office365 account?

    • Hi
      I haven’t heard of a specific limit to shared mailboxes. But it would be interesting to hear. But I would not worry. Do you have a lot of Shared mailboxes ?

      • Not yet, but we are working on an application and I am just checking possible scenarios

  13. Hi I’ve just tried to give a shared mailbox delegate permissions to a resource mailbox (Receptionists Group to a meeting room). I am unable to pick the shared mailbox it appears only user mailboxes is this by design I’m sure I could do this in exchange 2010. (Exchange 2013) Is this something that has changed in 2013 in preparation to O365 migration? Something to do with licensing perhaps…

  14. What is the RecipientLimits for Shared mailbox?
    When we run the command it lists as unlimited.
    RecipientLimits : Unlimited

    For user mailbox the limit is set as 500

  15. Someone above has suggested using IMAP to connect to shared mailboxes . While that is a novel idea, it requires too much effort when you have A large number of users to support .

    I will look into it however. Our Organization had to use licensed mailboxes versus free shared ones so that users could attach their mobile devices and/or retain larger amounts of data . What we have done this year to save money was convert the type of license down to exchange E1 license. So while not free significantly cheaper per mailbox.

    Slightly off-topic : Not exchange 2016 is ready to be deployed on prem. Is anyone aware if the permissions issue between on prem and office 365 has been resolved so that we could keep our shared mailboxes on prem and be accessible to online userS?

  16. HI Peter!

    I have a security issue/licensing question if you know the answer to it I would be more than grateful.

    We are licensing a customer with Exchange online plan 1. This license includes a service called “Exchange online protection” and on top of that we will be selling them Advanced Thread Protection which is USER license. Now the discrepancy question. Does the customer need to buy EXTRA EOP and ATP licenses for Shared Mailbox ?

    TechNet says:

    What are the license requirements for shared mailboxes?
    Shared mailboxes need to be licensed for Advanced Threat Protection. For example:
    • A company has five 5 users in Office 365. Each user has a mailbox, and there is one shared mailbox. This company will need a license for:
    o 6 seats of Exchange Online Protection (5 users + 1 shared mailbox)
    o 6 seats of Advanced Threat Protection (5 users + 1 shared mailbox)

    How can this be correct since Plan 1 and ATP are both USER licenses and we are licensing a USER not mailbox.

    Thank you and best regards

    • Hi, I never heard that about licensing the Shared Mailboxes before. I would create a support ticket with Office 365 support, to get this confirmed, if I was you.

  17. Hi Peter,

    I have a shared mailbox which i send all my backup e-mails to. this is monitored using PRTG software which works for aprrox 20 mins then they all get the same error (all 117 of them) saying they cannot access mailbox.

    Do you know how we can get outlook365 to accept more reads to the mailbox as i have been told the maximum is 20.

    after the initial sensors have checked the mailbox they go green but after 20 mins they all start going red with this access Pe124 alarms.

    as we would like to monitor using PRTG and this one mailbox this is stopping us going any further with this problem.

    any ideas??

    • Hi Mike

      Not sure about this, you would properly have to contact MS support through your Office 365 tenant on this and see if they can do anything about this.


  18. There was a previous comment created here:

    Harm on September 1, 2016 8:52 am
    Shared Mailboxes are free, but what is the maximum number of shared mailboxes that can be added to a Office365 account?

    You indicated you are unaware of a limit a year ago.

    Have circumstances changed or have you come across more information about the limit to the number of shared mailboxes?

    To my understanding, the limiting factor is performance based versus the number of mailboxes.

  19. Hi Peter
    We are facing performance issue. 10 user’s are using shared mail box.
    How many members can use shared mail box in OWA .
    what is the user limitation of shared mail box.

  20. Hi All,

    Is there any way to prevent/restrict access to online archive mailbox on shared mailbox.

  21. We have noticed that when we perform the following action using our O365 Shared Mailbox we receive an NDR stating that their is a 4GB limit for sending emais.

    Secnario – My mailbox is in O365, when I try and do a Send As from a shared O365 mailbox to an on premise email address, we receive the 4GB NDR…. Do you know if this is a limitation of Shared mailboxes and where this 4GB limit would be set?

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