We have a resource mailbox calendar that has a security group ("group A") set as an owner of the calendar folder. Members of that group are still unable to see/add calendar items as an owner. Another group ("group B") is also added as owner and I'm a member of that group - I am able to see/add items as an owner as expected. Any thoughts on why the trouble with the "group A"? Both groups are mail-enabled Universal Security groups in AD.
1. Try removing the permissions of the SG1 and then wait for approx 15 minutes.
2. Then run Get-MailboxFodlerPermission mailbox:\Calendar (see the results if the SG1 has been removed from the Permissions)
3. Ideally Permissions are defined via ACL, so without permission over the Mailbox itself, i don't think your SG1 members would be able to access Calendar folder only. THis functionality does works when a Mailbox is given permission over calendarfolder of another mailbox, but with Security Groups you would have give atleast Read access on the Mailbox itself first before giving access over Calendar Folder.