How to Archive a Shared Mailbox in Microsoft 365 (2026)

How to Archive a Shared Mailbox

To archive a shared mailbox in Microsoft 365, assign it an Exchange Online Plan 2 licence (or an Exchange Online Plan 1 licence plus the Exchange Online Archiving add-on), then enable the In-Place Archive on the mailbox. Without one of those licences, a shared mailbox has no archive - and the mailbox itself is capped at 50 GB.

That is the direct answer, but it is usually not the whole question. "Archive a shared mailbox" means three different things depending on what you are actually trying to do:

1. The shared mailbox is filling up and you need more room - that is the In-Place Archive scenario above.
2. The shared mailbox is being retired and you need to keep its contents for compliance - that is the inactive mailbox or export scenario.
3. You converted a departed employee's mailbox to a shared mailbox to avoid paying for a licence, and now it is growing past the limits - that is the departed-user scenario, and there is a cleaner pattern for it.

This guide covers all three, with the licence rules as Microsoft currently documents them.

The 50 GB Reality: Shared Mailbox Limits in 2026

Per Microsoft's current documentation, a shared mailbox can store up to 50 GB of data without a licence. Beyond that, the rules are:

What you want	What Microsoft requires
Shared mailbox over 50 GB (up to 100 GB)	Exchange Online Plan 2 licence assigned to the shared mailbox
In-Place Archive on a shared mailbox	Exchange Online Plan 2, or Exchange Online Plan 1 + Exchange Online Archiving add-on
Auto-expanding archive (up to 1.5 TB)	Same licences as In-Place Archive - either one enables it
Litigation hold on a shared mailbox	Exchange Online Plan 2, or Exchange Online Plan 1 + Exchange Online Archiving add-on
Retention policies, eDiscovery (Premium), Defender for Office 365	The shared mailbox must be licensed for each such feature

Source: Microsoft's shared mailbox documentation and Exchange Online limits.

Two quirks worth knowing:

• What happens at the cap: when a shared mailbox hits its storage limit it can still receive email for a while but cannot send. Eventually it stops receiving too, and senders get non-delivery reports. Shared mailboxes at their cap fail quietly - nobody is signed into them to see the warnings.
• The pre-2018 exception: unlicensed shared mailboxes created before July 2018 have a 100 GB limit rather than 50 GB, a legacy of a provisioning change Microsoft made that year.

Option 1: Enable the In-Place Archive (Mailbox Is Filling Up)

If the shared mailbox is active and simply growing, the supported path is Microsoft's own In-Place Archive:

1. Assign the licence. Either an Exchange Online Plan 2 licence, or an Exchange Online Plan 1 licence plus the Exchange Online Archiving add-on, assigned directly to the shared mailbox's account.
2. Enable the archive. In the Exchange admin center, open the shared mailbox and enable the mailbox archive (also possible through Exchange Online PowerShell). Once enabled, the mailbox gets an archive that starts at 100 GB.
3. Let retention move the mail. Exchange moves older items into the archive automatically based on the retention policy applied to the mailbox - users with access to the shared mailbox see the archive as a separate folder tree.
4. Enable auto-expanding archiving if needed. With either qualifying licence, the archive can auto-expand incrementally up to 1.5 TB as it fills.

The economics are worth checking before you commit: an Exchange Online Plan 2 licence is an ongoing per-mailbox cost, forever, for every shared mailbox that needs one. A tenant with dozens of over-limit shared mailboxes is quietly accumulating a licensing bill for mailboxes that no human owns. For the full picture of what Exchange Online Archiving does and does not cover, see Exchange Online Archiving: costs, coverage, and gaps.

Option 2: Retire the Shared Mailbox but Keep the Data

If the shared mailbox has reached the end of its life - a closed project, a discontinued support address - and you need its contents preserved:

• Inactive mailbox. Place the mailbox on hold, then delete the account. The mailbox becomes an inactive mailbox that Microsoft preserves without an ongoing licence. The catch: placing the hold in the first place requires the mailbox to be licensed for it (the same Exchange Online Plan 2 or Plan 1 + Archiving add-on rule), and inactive mailbox content still counts toward tenant storage. For the full comparison of when to use each mailbox type, see inactive vs shared vs archive mailbox.
• PST export. Exporting to PST via eDiscovery and storing the file somewhere cheap is the traditional path. It works, but PSTs are fragile, unsearchable at scale, easy to lose, and a poor answer when legal asks for the mailbox three years later.
• Third-party archive to your own storage. Archive the mailbox contents into your own Azure Blob Storage in a searchable, auditable form, then delete the mailbox entirely. This is the pattern Chipmunk automates for departed-user mailboxes - the same preservation logic applies to a shared mailbox being retired.

Option 3: The Departed-User Pattern (And Its Hidden Costs)

The most common reason enterprises end up with oversized shared mailboxes: converting departed employees' mailboxes to shared mailboxes to avoid paying for the licence. It is a well-known workaround - the conversion is free, the mail is retained, and the licence goes back in the pool.

The hidden costs show up later:

• The converted mailbox is now subject to the 50 GB unlicensed cap. Long-tenured employees often leave with mailboxes larger than that - which means assigning a licence anyway, defeating the point.
• No litigation hold and no retention-policy coverage without a licence, which is precisely the coverage legal expects on a departed employee's mail.
• The mailbox accumulates forever. Five years of departures handled this way leaves a tenant with hundreds of orphan shared mailboxes that nobody owns, reviews, or dares delete.

The cleaner pattern is to archive the departed user's mailbox properly at offboarding time instead of converting it. Chipmunk detects disabled accounts in Microsoft Entra ID and automatically archives the user's Exchange Online mailbox - along with their OneDrive and Teams data - into your own Azure Blob Storage. The archive is searchable and auditable, the data is in storage you own, and the licence is reclaimed without leaving an orphan mailbox behind. The full workflow is covered in the Microsoft 365 departed user archiving guide and the licence-cost side in stop paying for Microsoft 365 licences after staff leave.

Frequently Asked Questions

Does a shared mailbox need a licence to have an archive?

Yes. Per Microsoft's documentation, enabling the In-Place Archive on a shared mailbox requires an Exchange Online Plan 2 licence, or an Exchange Online Plan 1 licence with the Exchange Online Archiving add-on. Either licence also allows auto-expanding archiving.

How big can a shared mailbox archive get?

The archive starts at 100 GB. With auto-expanding archiving enabled, Microsoft adds storage incrementally up to 1.5 TB, which includes the Recoverable Items folder.

What happens when a shared mailbox is full?

It degrades in stages: first it can receive but not send, then it stops receiving entirely and senders get non-delivery reports. Because nobody signs into a shared mailbox directly, the quota warnings often go unseen until external senders start reporting bounces.

Can I put a shared mailbox on litigation hold?

Only with a licence - the same Exchange Online Plan 2 or Plan 1 + Exchange Online Archiving add-on requirement as the archive. An unlicensed shared mailbox cannot be placed on litigation hold.

Is converting a departed user's mailbox to a shared mailbox a good archiving strategy?

It works as a short-term licence-recovery tactic, but it is a poor archive: the mailbox is capped at 50 GB unlicensed, has no hold or retention coverage without a licence, and accumulates as an unowned object in the tenant indefinitely. For departures, archiving the mailbox to your own storage at offboarding time - then deleting it cleanly - is the pattern that satisfies both finance and legal.

How many users can access a shared mailbox?

Microsoft supports a maximum of 25 users per shared mailbox. Beyond that, users can hit connection failures or duplicated messages, and Microsoft recommends a Microsoft 365 group instead.

Related Guides

• Inactive vs shared vs archive mailbox: which to use - the three mailbox types admins constantly confuse, compared.
• Exchange Online Archiving: costs, coverage, and gaps - what Microsoft's EOA actually covers.
• Microsoft 365 departed user archiving - the offboarding workflow that avoids the shared-mailbox conversion trap.
• Stop paying for Microsoft 365 licences after staff leave - the licence-cost side of the same problem.