Excluding Inactive Mailboxes from Org-Wide Retention Holds

Sometimes You Want to Get Rid of Inactive Mailboxes

Sometimes Microsoft doesn’t communicate changes made to PowerShell cmdlets that introduce interesting new functionality to Office 365. There’s so much change in the service that they could be forgiven for an occasional slip-up, unless of course you need to use the specific feature that is undocumented.

New Parameters for Set-Mailbox

Which brings me to the well-known Set-Mailbox cmdlet, which boasts two parameters called ExcludeFromOrgHolds and ExcludeFromAllOrgHolds, a fact highlighted by MVP Vasil Michev in his ongoing crusade to discover what’s hidden in the corners of Office 365.

These parameters allow administrators to exclude some or all org-wide retention holds from inactive mailboxes. Remember that an inactive mailbox is one belonging to an Office 365 account that has been deleted but is kept because a hold exists on the mailbox. The hold can be any form of hold supported by Exchange Online, including litigation holds and those set by Office 365 retention policies. Retention holds come in two flavors, org-wide and non-org-wide (in other words, holds that apply to all mailboxes and those that apply to selected mailboxes).

Excluding an org-wide hold means that when Exchange evaluates whether to keep an inactive mailbox, it ignores that hold. If all org-wide holds are ignored, the inactive mailbox will only be kept if a specific non org-wide hold exists.

Controlling Org-Wide Holds on Inactive Mailboxes

Why do these parameters exist? Well, Microsoft introduced inactive mailboxes several years ago as a way for organizations to keep mailboxes around for compliance purposes without having to pay for Office 365 licenses. The most common use case is when mailboxes are kept for ex-employees. The idea is that a tenant will apply a hold to keep the mailboxes inactive for the desired period and then release the hold when the mailboxes are no longer needed.

Org-wide holds apply to both active and inactive mailboxes. Over time, it’s possible that a tenant will add new org-wide holds. The effect is that the set of inactive mailboxes is likely to grow because any mailbox that is deleted will become inactive because one or more org-wide holds exist.

Keeping inactive mailboxes is good if intended. It’s not so good if you don’t want or need those mailboxes. One of the principles of data governance in Office 365 is that tenants should be able to decide what data to keep and what to remove, and keeping inactive mailboxes longer than they should be goes against that principle. I imagine that Microsoft introduced these cmdlets to give tenants the ability to decide what org-wide holds should apply to inactive mailboxes.

Discovering Org-Wide Holds

Org-wide holds are registered in the Exchange Online organization configuration. To see the set, run the PowerShell command:

The holds we’re interested in start with mbx. Those starting with grp apply to Office 365 Groups. The values following are GUIDs that point to the retention policies defining the holds. If you’re interested in understanding how to resolve the GUID to find the retention policy, see Chapter 19 of the Office 365 for IT Pros ebook.

Excluding Org-Wide Holds from Inactive Mailboxes

To exclude specific org-wide holds from a mailbox, run the Set-Mailbox cmdlet and pass the GUIDs for the holds you want to exclude in a comma-separated list for the ExcludeFromOrgHolds parameter. Use the same format for the GUIDs as reported by Get-OrganizationConfig. When you run the command, Exchange updates the InPlaceHolds property for the mailbox to note the excluded holds.

Microsoft recommends that you use the distinguished name or ExchangeGUID property to identify the mailbox. This is to be absolutely sure that a unique value is passed because if you exclude the holds for the wrong inactive mailboxes, you run the risk that Exchange will remove these mailboxes permanently when it evaluates the holds that exist on them.

To remove all org-wide holds from a mailbox, run Set-Mailbox and pass the ExcludeFromAllOrgHolds parameter. Because you’re now removing all org-wide holds, it’s even more important to be certain that you’re processing the right mailboxes.

The Effect of Exclusion

I wrote a script to exclude all org-wide holds from the inactive mailboxes in my tenant. Immediately Set-Mailbox processed a mailbox, Exchange evaluated the holds to decide whether to remove the mailbox. After the script finished, the number of inactive mailboxes reduced from 39 to 17. This proves that you need to be ultra-careful when you exclude any org-wide hold from an inactive mailbox.


For more information about managing Exchange Online mailboxes, read Chapter 6 in the Office 365 for IT Pros eBook to discover even more valuable tips and techniques.

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