Guide · Offboarding
The standard advice stops working at 50 GB, exactly where the mailboxes you most want to keep already are. Four options, what each costs, which one fits which situation, and the rule that avoids all of it.
By Alex Makey · 6 September 2026 · 6 min read · Verified against Microsoft documentation, September 2026
The standard advice for a leaver’s mailbox is “convert to shared, remove the licence”. It stops working at 50 GB, and for the people whose mail you most want to keep — long-serving, senior, client-facing — 50 GB is often where the mailbox already is. Here are the four options for the large ones, what each costs, and how to choose.
A shared mailbox is free up to 50 GB. Above that, or if it has an archive, or if it is placed on litigation hold, it needs an Exchange Online Plan 2 licence. So the free route closes exactly for the mailboxes with the most history in them.
Check first. Get-MailboxStatistics user@contoso.com | Select TotalItemSize for the primary mailbox, and Get-MailboxStatistics user@contoso.com -Archive if there is an archive. Add them together; the archive counts.
Place the mailbox on hold while it is licensed, then remove the licence. It becomes an inactive mailbox: invisible in the address book, costing nothing, retaining everything for as long as the hold lasts, searchable and exportable through eDiscovery.
What it does not give you: day-to-day access. Nobody can open an inactive mailbox in Outlook. To read something in it, you run an eDiscovery search or restore the mailbox. That makes it the right answer for compliance and legal retention, and the wrong answer for “the manager needs to answer his old emails”.
Requires Exchange Online Plan 2 (in E3 and E5) at the moment the hold is set. Hold first, licence removal second; the other order purges the mailbox.
Get the mailbox under 50 GB, then convert. The trimming is usually easy: export the archive or the oldest years to PST, delete them from the mailbox, convert, remove the licence. The exported years sit in a PST on a file share or in SharePoint, searchable by whoever inherits the work.
What it gives you: free ongoing access to the recent years in Outlook, which is what the successor actually needs. What it costs: an hour of administration and a PST that has to be looked after. The right answer for most senior leavers.
Convert to shared and leave an Exchange Online Plan 2 licence on it. That is a few euros a month rather than the full Business Premium or E3 the person had. Everything stays, everyone who needs access has it in Outlook, nothing is exported.
The right answer when the mailbox is genuinely in daily use by a successor — a shared sales or client mailbox that happened to live under a person’s name — and the wrong answer if it is kept “just in case”, because just in case lasts forever and so does the invoice.
Export the whole mailbox to PST, store it where the company stores records, delete the account. No licence, no Exchange object, nothing to review next year.
Right for leavers whose mail has no ongoing business value and no retention obligation. Wrong for anyone client-facing, anyone in a regulated role, or anyone leaving under a cloud, because a PST on a file share is not a defensible legal hold.
Decide before the licence is removed, not after. Every option above is available while the mailbox is licensed and most of them are not once it is soft-deleted. The thirty-day grace period is long enough to restore a licence and fix a mistake; it is not long enough to discover the mistake in the first place if nobody is looking.
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Related questions
Yes, but it will need an Exchange Online Plan 2 licence to stay shared above 50 GB. Alternatively trim it below 50 GB by exporting older mail to PST first, then convert and remove the licence.
An inactive mailbox is created by placing a hold and removing the licence: free, retains everything, searchable through eDiscovery, but not accessible in Outlook. A shared mailbox is accessible in Outlook by anyone granted permission, free up to 50 GB.
A shared mailbox with an in-place archive needs an Exchange Online Plan 2 licence regardless of size. Check both the primary mailbox and archive sizes before deciding.
No. A PST on a file share can be altered or lost and is not a defensible retention mechanism. Where legal or regulatory retention is required, place the mailbox on litigation hold before removing the licence.
Place the mailbox on hold while it is still licensed and decide later. The hold is reversible and costs nothing once the licence is removed; the purge after the grace period is permanent.
Rather not do this yourself?
Describe the situation and you get back a sequence, an honest view of what will be slow, and a fixed price — usually within one business day. Or ask one question and get one answer.