Making room calendars visible and editable in Outlook (Exchange admin)

Why this is needed

When i-Reserve writes a booking to Outlook in room mode (app-only), the appointment is created directly in the calendar of the room mailbox. By default a resource mailbox's calendar permissions are set to AvailabilityOnly: colleagues only see busy/free, not the subject or details. If you want staff to see the title and content of the room bookings - or even be able to edit them - you adjust the room mailbox's calendar permissions. This can only be done through Exchange Online PowerShell; the Microsoft 365 admin center has no button for it.

Audience: the Exchange / Microsoft 365 administrator. Your account needs the Exchange Administrator (or Global Administrator) role.

Cases you are likely to hit

• The room shows "Busy" in Outlook, but colleagues see no subject - permissions are on AvailabilityOnly.
• You want a planner to also be able to edit the room bookings in Outlook - this requires a higher permission (Author/Editor).
• You want to see the room calendar alongside your own in Outlook.
• For a Dutch-language mailbox the calendar folder is called Agenda instead of Calendar, so commands on :\Calendar fail.

Which permission level do you choose?

Recommendation: set Default (everyone) to at most Reviewer (view), and grant edit rights deliberately to a specific planner or group only. See the synchronisation warning at the bottom.

Setting up Exchange Online PowerShell

Windows

Install-Module ExchangeOnlineManagement -Scope CurrentUser
Connect-ExchangeOnline -UserPrincipalName admin@customer.onmicrosoft.com

Confirm the NuGet provider installation or trusting the PSGallery with Y if asked. Connecting opens a browser for sign-in (with MFA).

macOS

On a Mac you use PowerShell 7. Install it first via the Terminal:

brew install --cask powershell

If the stable cask is unavailable, use brew install --cask powershell@preview (the command is then pwsh-preview instead of pwsh), or download the macOS .pkg from Microsoft's PowerShell releases page. Then start PowerShell and install the module:

pwsh
Install-Module ExchangeOnlineManagement -Scope CurrentUser
Connect-ExchangeOnline -UserPrincipalName admin@customer.onmicrosoft.com

The modern module works on macOS; sign-in goes through the browser (MFA). If pwsh is not recognised right after installing, open a new Terminal window.

Setting the permissions

View current permissions:

Get-MailboxFolderPermission -Identity room2@customer.onmicrosoft.com:\Calendar

Set Default to Reviewer (everyone sees title + details):

Set-MailboxFolderPermission -Identity room2@customer.onmicrosoft.com:\Calendar -User Default -AccessRights Reviewer

Grant edit rights to a specific planner (instead of everyone):

Add-MailboxFolderPermission -Identity room2@customer.onmicrosoft.com:\Calendar -User planner@customer.onmicrosoft.com -AccessRights Editor

Use Set- to change an existing permission (such as Default); use Add- to add a new user.

Dutch-language mailbox: the folder is called "Agenda"

If :\Calendar fails, the mailbox language is Dutch and the folder is called Agenda. Determine the folder name automatically:

$cal = (Get-MailboxFolderStatistics room2@customer.onmicrosoft.com -FolderScope Calendar | Where-Object FolderType -eq 'Calendar').Name
Set-MailboxFolderPermission -Identity "room2@customer.onmicrosoft.com:\$cal" -User Default -AccessRights Reviewer

All rooms at once

"room1","room2","roomA","roomB" | ForEach-Object { Set-MailboxFolderPermission -Identity "$_@customer.onmicrosoft.com:\Calendar" -User Default -AccessRights Reviewer }

Preserving the subject (optional)

Resource mailboxes replace the subject with the organiser's name by default. Because i-Reserve writes the appointment directly into the mailbox, that processing usually does not run - but to be sure:

Set-CalendarProcessing -Identity room2@customer.onmicrosoft.com -AddOrganizerToSubject $false -DeleteSubject $false -DeleteComments $false

Adding the room calendar in Outlook

• Outlook on the web / new Outlook: Calendar → Add calendar → Add from directory → type the room mailbox → add.
• Classic Outlook (desktop): Calendar → Open Calendar → From Address Book → select the room.

Enable several rooms and use Schedule view to see them side by side.

Note: synchronisation and source of truth

i-Reserve synchronises bidirectionally with the room calendar. If you give staff edit rights (Editor/Author), keep the following in mind:

• A change made in Outlook is pulled back into i-Reserve through the inbound synchronisation (depending on the inbound settings).
• A subsequent outbound update from i-Reserve can overwrite a manual Outlook change again.

So decide up front whether i-Reserve or Outlook is leading. For most situations Reviewer (read only) is the safest default.