Shared Mailbox Retention, Sent-Item Auditing, and a 41 GB Capacity Crunch
Northwind's 12-person procurement team uses a shared mailbox, [email protected], now at 41 GB, alongside individual mailboxes. Two coordinators have Full Access and Send As. Three problems surfaced this week. First, a retention policy that should remove items older than three years is deleting nothing from the shared mailbox, although it works in the coordinators' own mailboxes. Second, replies the coordinators send as the shared mailbox appear only in their personal Sent Items, so the team cannot audit commitments. Third, the mailbox is approaching the 50 GB limit, and the admin proposes enabling AutoArchive at six months and archiving to a local PST on one coordinator's PC. Meanwhile, one coordinator's Outlook shows only 12 months of mail while another shows the full history. The team wants to keep all purchasing records for seven years for audit but reduce the live mailbox size.
1. The three-year retention policy works in personal mailboxes but not in the shared mailbox. What is your diagnostic sequence, and what is the most likely cause?
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Start by separating mailbox-level, folder-level, and item-level scope. In Exchange Online, a retention policy is assigned to a mailbox, not to a user; shared mailboxes can carry their own policy. Confirm the shared mailbox has the policy assigned and that the policy contains a delete tag, not only an archive tag. Then check folder inheritance: a folder or individual item can have an explicit tag that overrides the inherited default, and items with a personal tag are exempt from the default. Also check the action type: an archive tag moves items to the Online Archive and leaves the mailbox size roughly unchanged, which would explain 'nothing deleted.' Run the Managed Folder Assistant and review the mailbox's retention report. Most likely, the shared mailbox was never assigned the policy, or its folders carry an explicit 'never delete' tag. Assignment and tag override are the first two checks; changing the policy before confirming those is guesswork.
2. How do you make replies sent as the shared mailbox auditable, and what trade-offs do the options carry?
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The default behavior is by design: when a delegate sends As or Send on Behalf, the copy lands in the delegate's Sent Items, not the shared mailbox. Exchange Online has two mailbox settings, MessageCopyForSentAsEnabled and MessageCopyForSendOnBehalfEnabled; enabling them writes a copy into the shared mailbox's Sent Items while preserving the delegate's own copy. That gives the team a single audit trail and keeps individual accountability. The trade-off is duplication and potential confusion: the shared mailbox Sent Items grows faster, and a delegate may see the same message twice if both mailboxes are open. Also decide whether delegates need Send As (message appears from the shared address, no delegate name) or Send on Behalf (recipient sees 'on behalf of'), because the audit and recipient experience differ. Test with one coordinator before enabling for both.
3. The admin proposes AutoArchive at six months to a PST. Evaluate this against alternatives for a 41 GB shared mailbox that must retain seven years of records.
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AutoArchive is a client-side feature: it runs only while Outlook is open, applies per-folder settings, and moves items to a local PST. On a shared mailbox that is a poor fit. The PST lives on one PC, is not backed up centrally, is invisible to the other coordinator, and does not reduce the Exchange mailbox if the archive target is local only. It also creates a seven-year records problem: a PST is not an auditable, searchable repository. Better options: enable an Exchange Online Archive for the shared mailbox, subject to licensing and mailbox/archive limits, assign an archive retention policy that moves items older than, say, one year to the archive, and keep a separate delete or review policy aligned to the seven-year requirement. If the archive is unavailable, increase capacity or split the mailbox by year, but do not treat a desktop PST as the system of record. Verify with a pilot and eDiscovery search.