Resource Mailboxes Wrongly rejecting bookings

Question

We are using hybrid Exchange and have recently migrated our mailboxes to Exchange online and are having trouble getting resource mailboxes to accept bookings correctly.

We would like bookings from a group of users to be automatically accepted and other requests to be rejected. These users have all been put in a mail-enabled security group which only exists online.

The calendar processing settings are shown below (with the group names changed). Users who are a member of the group in the BookInPolicy get their bookings declined with this message:

Your meeting request was declined.

You don't have permission to book this resource.

I'm sure I'm missing something simple but I can't see why this is failing.

AutomateProcessing                   : AutoAccept
AllowConflicts                       : False
AllowDistributionGroup               : True
AllowMultipleResources               : True
BookingType                          : Standard
BookingWindowInDays                  : 8
MaximumDurationInMinutes             : 10080
MinimumDurationInMinutes             : 0
AllowRecurringMeetings               : False
EnforceAdjacencyAsOverlap            : False
EnforceCapacity                      : False
EnforceSchedulingHorizon             : True
ScheduleOnlyDuringWorkHours          : False
ConflictPercentageAllowed            : 0
MaximumConflictInstances             : 0
ForwardRequestsToDelegates           : True
DeleteAttachments                    : True
DeleteComments                       : True
RemovePrivateProperty                : True
DeleteSubject                        : True
AddOrganizerToSubject                : True
DeleteNonCalendarItems               : True
TentativePendingApproval             : True
EnableResponseDetails                : True
OrganizerInfo                        : True
ResourceDelegates                    : {XXXXXXXXXXXXXXXXXXX}
RequestOutOfPolicy                   : {}
AllRequestOutOfPolicy                : False
BookInPolicy                         : {/o=ExchangeLabs/ou=Exchange Administrative Group (XXXXXXX)/cn=Recipients/cn=XXXXXXXXXXXXXXXXXXXXXXXXXXXXX}
AllBookInPolicy                      : False
RequestInPolicy                      : {}
AllRequestInPolicy                   : False
AddAdditionalResponse                : False
AdditionalResponse                   : 
RemoveOldMeetingMessages             : True
AddNewRequestsTentatively            : True
ProcessExternalMeetingMessages       : True
RemoveForwardedMeetingNotifications  : False
AutoRSVPConfiguration                : Microsoft.Exchange.Data.Storage.AutoRSVPConfiguration
RemoveCanceledMeetings               : False
EnableAutoRelease                    : False
PostReservationMaxClaimTimeInMinutes : 10

Answer 1

Why is the ResourceDelegates : {XXXXXXXXXXXXXXXXXXX} defined if are allowing the group to book automatically?

Answer 2

Hi，@AdamBarnes-5693

Thanks for posting your question in the Microsoft Q&A forum.

According to the information you provided, there is an error in your settings.

You can refer to this link for details：https://learn.microsoft.com/en-us/powershell/module/exchange/set-calendarprocessing?view=exchange-ps

If my answer is helpful to you, please mark it as the answer so that other users can refer to it. Thank you for your support and understanding.