Keep a copy of sent emails for delegates of user mailboxes!

The ability to send messages on behalf of somebody else has been around for a long time, but it has it quirks. One of the major issues with it was the fact that any messages send on behalf of say a shared mailbox weren’t copied to the mailbox, thus other people working with it were unaware of the action. Over the course of the last few years and Exchange versions, Microsoft offered us different workarounds for this issue, the latest one being the use of the MessageCopyForSentAsEnabled and MessageCopyForSendOnBehalfEnabled parameters. For a brief overview on the different methods and details on said parameters you can refer to the EHLO blog post here:

As you can see from the article above, while the new method proved very useful and easy to control, it was only available for shared mailboxes. If you tried to configure the setting for any user mailbox, you were greeted by the following error message:

PS C:\> Set-Mailbox huku -MessageCopyForSendOnBehalfEnabled $true -MessageCopyForSentAsEnabled $true

MessageCopyForSentAsEnabled can only be set on shared mailboxes

+ CategoryInfo : NotSpecified: (huku:MailboxIdParameter) [Set-Mailbox], TaskArgumentException

+ FullyQualifiedErrorId : [Server=HE1PR03MB1340,RequestId=e7ba59bb-a4a4-4de8-b751-1904ac73185c,TimeStamp=11/11/2015 8:34:59 PM] [FailureCategory=Cmdlet-TaskArgumentException] 36931497,Microsoft.Exchange.Management.RecipientTasks.SetMailbox

This in turn meant that we still had to address issues with delegates for user mailboxes, say a secretary sending mail on behalf of a VP. Well, no more! The parameters can now be used for both shared and user mailboxes. For example, to turn this on for a single user mailbox you can use:

Set-Mailbox HuKu -MessageCopyForSendOnBehalfEnabled $true -MessageCopyForSentAsEnabled $true

To turn the settings on for all user mailboxes, use:

Get-Mailbox -RecipientTypeDetails UserMailbox | Set-Mailbox -MessageCopyForSendOnBehalfEnabled $true -MessageCopyForSentAsEnabled $true

To turn the settings on for all user and shared mailboxes:

Get-Mailbox -RecipientTypeDetails UserMailbox,SharedMailbox | Set-Mailbox -MessageCopyForSendOnBehalfEnabled $true -MessageCopyForSentAsEnabled $true

If you try to turn it on for any other type of mailbox, you will still run into the familiar error message:

MessageCopyForSentAsEnabled can only be set on shared mailboxes or user mailboxes.

+ CategoryInfo : NotSpecified: (WC:MailboxIdParameter) [Set-Mailbox], TaskArgumentException

+ FullyQualifiedErrorId : [Server=DB6PR0302MB2614,RequestId=602ce875-59c1-4353-8fd5-d37bc8565572,TimeStamp=12/23/2016 8:36:24 AM] [FailureCategory=Cmdlet-TaskArgumentException] 10E0541D,Microsoft.Exchange.Management.RecipientTasks.SetMailbox

One last remark: at the time of this writing, the functionality is not yet rolled out fully, so while you can configure the settings, the actual copies of the sent emails don’t get copied to the mailbox. Which I guess is why Microsoft hasn’t yet announced this officially πŸ™‚

22 thoughts on “Keep a copy of sent emails for delegates of user mailboxes!

  1. Jacob says:


    I have enabled this through powershell exchange online (O365) and it works, but it seems like I am getting duplicates. I’m getting two messages saved in the sent items folder for the delegator. Can anyone suggest anything to try/help?


  2. Ken says:

    Hi folks,

    I’m on on-prem Exchange 2016 (build 15.01.1034.026 – which is CU6). Unfortunately after running

    MessageCopyForSentAsEnabled : True
    MessageCopyForSendOnBehalfEnabled : True

    on a shared mailbox, sent emails are still not going to the sent items folder of the shared mailbox.

    Please help! The users are killing me, they want it to be working and keep bugging me every day!

    – Ken

    1. stubbo says:

      Hi Ken –

      Did you ever get this working?

      Facing the same problem with EX2016 on-prem


  3. James Auman says:

    Do these commands work for Exchange 2013 CU16? When I run this command on a user mailbox:

    [PS] C:\Windows\System32>set-mailbox jb -messagecopyforsendonbehalfenabled $true

    I get this dreaded error:

    MessageCopyForSendOnBehalfEnabled can only be set on shared mailboxes

    1. Vasil Michev says:

      Afaik the feature is only planned for Exchange 2016.

  4. Munrakhan Ishaansingh says:

    Hello , can you guys confirm if setting these two parameters on 0365 will not solve the issue?

    Get-Mailbox -RecipientTypeDetails SharedMailbox | Set-Mailbox -MessageCopyForSendOnBehalfEnabled $true -MessageCopyForSentAsEnabled $true

    Is Microsoft team working on this issue?


    1. Vasil Michev says:

      For O365, the above cmdlets should work. For both Shared and User mailboxes.

  5. Lukas says:


    we use Exchange Server 2016 CU4 (15.01.0669.032) on-prem. We have an user mailbox that is used as additional mailbox by multiple users. I can set the command without no error. Here is the result:

    [PS] C:\Windows\system32>Get-Mailbox -Identity xyz | fl *MessageCopy*

    MessageCopyForSentAsEnabled : True
    MessageCopyForSendOnBehalfEnabled : True

    But nothing change. When I send an email from this mailbox it only appears in the sent items of the main user but not in the sent items of the additional mailbox.

    In Exchange 2010 it was working with the following command:
    [PS] C:\>Get-Mailbox xyz | Set-MailboxSentItemsConfiguration -SendAsItemsCopiedTo SenderAndFrom -SendOnBehalfOfItemsCopiedTo SenderAndFrom. After the migration to 2016 it stop working and the new command has no effect.

    I understand you right that that we have to wait some weeks because the rollout is still in progress? Thanks for reply.

    1. Vasil Michev says:

      Sorry, the rollout just started for Office 365/Exchange Online. Asking the PG (product group) now for plans for On-Prem Exchange, will let you know if they say something.

        1. Vasil Michev says:

          Should be coming in the next CU for On-Prem.

        2. Michael Mollard says:

          Do you have confirmation that this feature has NOT been included in Exchange 2016 CU5? The Powershell cmdlet exists, and I can modify User Mailboxes with :
          Set-Mailbox -Identity -MessageCopyForSentAsEnabled $True -MessageCopyForSendOnBehalfEnabled $True
          ..but it seems to have no effect.

        3. Vasil Michev says:

          They mentioned that it’s coming in CU6 and the previous KB should be pulled out now.

  6. Vasil Michev says:

    Just confirmed with the PG, the feature is now rolling to the service! Give it a few weeks as usual for rollout across the service!

    1. Lukas says:

      Sorry for the stupid question. PG stands for what? Please check my comment below also. Thanks!

  7. Leif says:

    Did you ever get a reply from the PG regarding the setting on a user mailbox in Office365?

    I can configure the MessageCopyForSentAsEnabled to True, but it doesn’t have any effect

    1. Vasil Michev says:

      Wasn’t working for me either in the service, I figured they must still be rolling the relevant bits. If it’s not working On-Prem either I guess they made some booboo with the code.

      I’ve sent a message to the PG to clarify on this, but nobody is around to answer because of the holidays πŸ™‚


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