Office 365 Calendar Meeting / Booking Length

Meeting rooms have become the main control for boardrooms having it automate the booking system, knowing who will be attending, how many users etc. There are companies which book meeting for very long period, some up to 3 years in advance. Most of the time, stand-alone environments will allow it. On Office 365, it is capped at 180 days. We will through the process of amending it. You can set it to Maximum of 1080 days.


  • Log onto the Office 365 Portal as a Tenant Admin.

  • Select the “Admin” tab.

  • Proceed to the “Exchange Admin Center” which is location on the left hand side under “Admin Centers

  • Then locate the “Resource Mailboxes”. You cannot set any mailboxes, groups or shared mailboxes under the GUI. Go to “Recipients” > “Resources”. You should see a list of your Room mailboxes.

  • You can double-click or highlight and select the pen icon to edit the Resource Mailbox.

  • Proceed to the “Booking Options”, edit the “Maximum Booking Lead Time (Days)” and then click “Save”.


This scenario is when you want to amend the booking time for a mailbox.

  • Connect to your Office 365 Tenant via Powershell
  • Once you are logging in, let us get a list of “Room” mailboxes. Run: Get-Mailbox <Idenity of mailbox> | Get-Calendarprocessing | fl . We are getting the mailbox information, then we are filtering for “CalendarProcessing” information. The FL ( Format list ) is to display all the information which we filtering for.

  • Output is as follows:

  • The Flag which we need to change is the “BookingWindowInDays

  • To set that flag, here is the command: Get-Mailbox ( Identity of the mailbox) | Set-CalendarProcessing -BookingWindowInDays 1080 . We are getting the mailbox information, then filtering for only “CalendarProcessing” information. But we appending the “Set” Flag. We are now setting the flag “BookingWindowInDays” . Thereafter you can add the number of days.

  • To check the information has been processed correctly, run the following command: Get-mailbox <Identity of the mailbox> | Get-CalenderProcessing | FL . Changes have been done.

Here is what happens if you try to set the flag to more than 1080 days. An error is advised.

Allow replication time for this.

Hope this helps.

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