Folder ACL exceeds allowed size

Copper Contributor

When trying to add a user as "Reviewer" to the calendar of a shared mailbox by


Add-MailboxFolderPermission -Identity <UserPrincipalName_SharedMailbox>:\Calendar -AccessRights Reviewer -User <UserPrincipalName_User>


PowerShell throws this error:


|Microsoft.Exchange.Data.Storage.ACLTooBigException|Folder ACL exceeds allowed size. (|Microsoft.Exchange.Data.Storage.ACLTooBigException|Folder ACL exceeds allowed size.)


The shared mailbox currently has 221 entries in the ACL (including "Default" and "Anonymous").

I tried this with a different mailbox on a different tenant and ran into the same error.


  1. Is there any documentation about this limitation?
  2. Is there a way to get around this limitation w/o putting all affected users in a group and assigning this group reviewer rights?
1 Reply
Every software has limits, in this case use (mail-enabled security) groups instead of adding each user individually.