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Outlook user gets a 'cannot send as' error when updating a meeting request

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I have just been trying to troubleshoot a user's issue, as follows:


When trying to update a meeting request they originated, they received the following NDR message from all recipients, including an external recipient:



"You can't send a message on behalf of this user unless you have permission to do so. Please make sure
you're sending on behalf of the correct sender, or request the necessary permission. If the problem continues, please contact your helpdesk."


Within Diagnostic Information for Administrators:





The issue appears to be similar to the following unresolved forum post:



I can't see how it will be related to the offline address book or Cached Exchange Mode if it also happens to an external recipient.  Something is going wrong somewhere.... Thanks in advance for any ideas anyone might have.
All Replies
  • Have you tried adding the send on behalf permissions through powershell?

    CEO - john doe

    PA - jane smith

    Set-Mailbox -Identity john doe -GrantSendOnBehalfTo jane smith

  • Sorry not to be as clear as I thought I was. The user is not sending on behalf of anyone, nor sending as them; all recipients give this message as though the user is trying to send as them instead of just sending to them.  The user can happily send email to the same users as they get the bounce from.  

    The bounce message lists each individual user and then the above 'You can't send a message on behalf of this user' text under each one.  Because of this, I've interpreted it as saying that it's somehow trying to send on behalf of the recipient.  I guess it's possible that it is having an issue sending on behalf of the user himself; I've asked him whether the meeting was originally created before his user was migrated to Office 365, as that could be a factor (his 'new' user trying to send as his 'old' user even though they're really the same person).  Otherwise, with the external user also showing the issue, I can't see how there's anything I can configure that would allow him to send to those people.

    I hope that makes more sense - thanks for your response.

  • Hi Dev,

    Before going further, I’d like to clarify the following details with this issue:
    1, How did your user update the Meeting request?
    2, Can this issue be reproduced with other users in your company, in addition, does this issue occur with OWA (Outlook Web App) or Outlook client.

    To update a meeting request, I’d like you can do this by refer to the following article:
    Modify a Meeting

    In addition, if the problem still persists, for us to better understand the problem, I’d like you can provide us the whole NDR message.

    Evan Zhang

  • I believe that the user used the same methods as you described, using the desktop Outlook client (PC).  

    As best I can work out, the issue is related to the fact that the meeting was created before the user was migrated from on-premises Exchange to Office 365.  

    The user can send other messages just fine.  I've not heard whether OWA worked (no reply yet from the user on this), but I suspect that it would have done.  This is the only time this has happened so far.

    I've advised the user to create a new meeting and have the recipients manually remove the old one.  If it is related to the migration, it won't happen too often and at least I know what it is.  I will keep an eye on it for future users who get migrated.



  • Hi Dev,

    Thanks for your update. As this issue doesn’t reoccur, it’s ok to resolve this issue by cancel the original meeting request and create a new one.

    In addition, you can refer to the following article to cancel a meeting request:
    Cancel a Meeting

    If you have any further questions regarding to this problem, please feel free to post them in this thread.

    Best Regards,
    Evan Zhang

  • I do not want to delete already made bookings. I have 100+ bookings in the caledar, some re-occuring and some not... I need to know, if I change the TimeZone, will the appointments, re-occuring or not be affected, will they change their time from say 11:00 (UTC) to 09:00 (GMT) for instance when the timezone is changed?

  • Hi NakedNuts,

    Are you in the same situation as Dev?

    Based on my test, if I changed the time zone of my computer, the re-occurring meetings would change their time to make sure the meeting occur at the same time as other attendees.

    If you have any other questions, It’s suggested to post you questions in a new thread so that we can follow up them more easily.


    Evan Zhang

  • I ran a test also, set up a new resource mailbox, entered some appts, gave myself full permission and changed the time zone a few times, I didnt get any changes to appt times with what ever time zone i chose.

    I believe the reason is, because it only matters what time zone the user is on and what time zone if the user choose when entering the appt, not the resource mailbox?

    I should be ok with this one any way due to the time zone being UTC - 0000 and the other being UTC 0000, just different place name.


    If you do find out that the time zone changes and why, I would be curious to know.

    Thanks for your help


  • Hi NN,

    Yes, the time zone changing of the resource mailbox won’t change the appointment time on the user side. In my test, I changed the time zone of my computer, it affected the appointment time showed in my Outlook client.

    Actually, when we schedule a meeting in Outlook client or OWA, the time zone information will be contained in the meeting request. When we send the meeting request to resource mailbox (to book the meeting room) or other recipient, the time zone information will be sent also, if the resource mailbox or recipient is not in the same time zone as we are, the meeting time will be converted. Therefore, whenever we schedule a meeting, we scheduled the meeting in a unique time.

    Evan Zhang


  • Having this same issue where the UserA tries to update an appointment after being migrated to O365 and they get a bounceback message stating 'You can't send a message on behalf of this user' under the name of each recipient in the meeting update. UserA is attempting to send a meeting update as themselves and not on behalf of any other user. There is no probem when UserA  sends emails to the recipients mentioned in the NDR, only the problem when sending updated meeting invitations. This is when they revieve the NDR. Can anyone provide information to help resolve this issue?

  • Hi IT Drummerboy,

    Based on my experience, the issue can be caused when the user was migrated but still use the old Outlook profile (or the user is migrated by using a PST file).

    In your situation, I suggest you do the following things to troubleshoot the issue:

    1) Check if the user can update the appointment in OWA (Outlook Web App)

    2) If the issue doesn’t occur, to resolve the problem, please re-create the Outlook profile for the user.

    For more reference:

    Connect Outlook to This Account

    Moreover, if my above information doesn’t help you, since this is an old thread, we recommend you post your questions in a new thread in the forum, so that we can follow up it more easily. Thanks for your understanding.

    Best Regards,

    Evan Zhang