Exchange Online Plan 1 vs Plan 2 is a choice between two standalone mailbox licences that look alike until something goes wrong: a mailbox fills up, a legal request arrives, or a leaver’s mail has to be kept. Most comparisons stop at “50 GB versus 100 GB” and a price, which is the least interesting difference. This post sets out what Microsoft Learn says each plan includes, the compliance features that only Plan 2 carries, when the Exchange Online Archiving add-on is the cheaper fix, and the failure modes that make the decision for you.
Both plans sit under the Microsoft 365 licensing guide, which covers the suites these standalone plans are carved out of. Every Microsoft fact below was checked against Microsoft Learn on 31 October 2026. I have not run this in production; my tenant is a lab, so what follows is the documentation read carefully, plus where I would expect it to bite. I have left out prices on purpose: they belong on Microsoft’s own pricing page and they change more often than the rules do.
Exchange Online Plan 1 vs Plan 2 at a glance
Plan 2 doubles the primary mailbox, turns a small archive into an auto-expanding one, and adds holds, Data Loss Prevention and inactive mailboxes. Plan 1 is a complete mailbox service without the compliance layer. The figures below come from the standalone plan columns of the Exchange Online limits service description and the feature table in the Exchange Online service description.
| Capability | Exchange Online Plan 1 | Exchange Online Plan 2 |
|---|---|---|
| User mailbox | 50 GB | 100 GB |
| Archive mailbox | 50 GB | 100 GB, auto-expanding to 1.5 TB |
| Exchange Online Archiving included | No (available as an add-on) | Yes |
| In-Place Hold and Litigation Hold | No | Yes |
| Microsoft Purview Data Loss Prevention | No | Yes |
| Inactive mailboxes | No | Yes |
| Shared mailbox it is assigned to | 50 GB | 100 GB |
| Manual retention policies, labels and tags | Yes | Yes |
| Microsoft Purview Message Encryption (Basic) | Yes | Yes |
| Journaling, transport rules, eDiscovery content search | Yes | Yes |
| Desktop Outlook rights | Not included | Not included |
The bottom row catches people out. Footnote 8 of the service description says connecting Exchange Online Plan 1 or Plan 2 to Outlook for Windows or Outlook for Mac requires those applications to be licensed first with an account that includes rights to the Microsoft 365 desktop apps. Neither plan gives you the desktop client. Outlook on the web and Outlook for iOS and Android are included in both.
Mailbox and archive storage: what the numbers mean
The storage gap is the difference most people buy Plan 2 for, and it is smaller than it looks for most users and larger than it looks for a few.
On Plan 1 the user mailbox is 50 GB and the archive is another 50 GB. On Plan 2 the user mailbox is 100 GB and the archive starts at 100 GB. With auto-expanding archiving turned on, Learn says storage is added incrementally once the 100 GB is reached, until the archive reaches 1.5 TB, and that 1.5 TB includes the Recoverable Items folder.
The capacity alerts follow the mailbox size. For Plan 1, Learn lists a warning at 49 GB, Prohibit Send at 49.5 GB and Prohibit Send/Receive at 50 GB. For Plan 2 the same thresholds are 98 GB, 99 GB and 100 GB. At Prohibit Send/Receive, Exchange Online rejects incoming mail and sends a non-delivery report to the sender. That is the moment a storage question becomes a business one, because customers are the people who see it first.
Two caveats from the same page. Administrators can reduce maximum mailbox sizes per user or globally, so the licence sets a ceiling rather than the actual quota. And Learn notes that the limits applied to an organisation may differ depending on how long it has been enrolled in the service, so check a real mailbox rather than assuming the table applies to yours.
Holds, DLP and inactive mailboxes: the compliance gap
This is the real difference in Exchange Online Plan 1 vs Plan 2. The service description lists In-Place Hold and Litigation Hold, Microsoft Purview Data Loss Prevention, and inactive mailboxes as Plan 2 features, and marks all three as not available on Plan 1.
- Holds. Litigation Hold preserves deleted items and the original versions of modified items until the hold is removed or a hold duration expires. Without it, a user who empties their Recoverable Items cannot be stopped from destroying evidence you are obliged to keep.
- Data Loss Prevention. DLP policies that inspect email for sensitive information are a Plan 2 feature in the Exchange table. On Plan 1 alone, the nearest tools are transport rules, which are included in both plans but are not a substitute for classifier-based DLP.
- Inactive mailboxes. These let you keep a leaver’s mailbox content after the account is gone. The limits page says a soft-deleted user mailbox is recoverable within 30 days. Past that window, on a plan without inactive mailboxes, the mail is gone.
Plan 1 is not a compliance-free licence. Manual retention policies, labels and tags, Messaging Records Management, journaling, S/MIME, eDiscovery content search and basic Message Encryption are all listed for both plans. What Plan 1 lacks is the ability to freeze a mailbox, to scan mail with DLP, and to keep a mailbox after its owner leaves.
When the archiving add-on beats Plan 2
If the only thing pushing you towards Plan 2 is storage or a hold, price Plan 1 with Exchange Online Archiving before you upgrade. The Exchange Online Archiving service description lists Exchange Online Plan 1 among the plans it can be added to, and says the add-on adds auto-expanding archiving, In-Place Hold and Litigation Hold. The same page lists Exchange Online Plan 2 among the plans that already include archiving and do not need the add-on.
What the add-on does not change is the primary mailbox. A Plan 1 user with Exchange Online Archiving still has a 50 GB primary mailbox and still hits Prohibit Send/Receive at 50 GB. The archive grows; the inbox does not. And DLP is not in the list of things the add-on adds.
| Need | Plan 1 + Exchange Online Archiving | Plan 2 |
|---|---|---|
| Large archive | Yes, auto-expanding | Yes, auto-expanding |
| Litigation Hold | Yes | Yes |
| Primary mailbox over 50 GB | No | Yes, up to 100 GB |
| DLP for email | Not listed | Yes |
So the rule of thumb is simple. If users fill their inbox, or the organisation needs email DLP, Plan 2 is the answer. If users keep years of mail they rarely open, or you need holds for a subset of mailboxes, the add-on on Plan 1 is the narrower purchase.
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Shared mailboxes and the Plan 2 exception
Shared mailboxes do not need a licence for normal use, but they are limited to 50 GB without one. Learn says that to raise the limit to 100 GB the shared mailbox must be assigned an Exchange Online Plan 2 licence, and that to place a shared mailbox on Litigation Hold it needs Plan 2 or Plan 1 with the Exchange Online Archiving add-on. Users who open a shared mailbox still need their own Exchange Online licence.
That makes Plan 2 a common purchase for mailboxes that have no user at all: a busy accounts inbox, a support queue, or a mailbox held for a dispute. If your Exchange Online Plan 1 vs Plan 2 decision is really about one large shared mailbox, license that mailbox and leave the users alone.
How the standalone plans relate to the suites
Most organisations do not buy Exchange Online on its own; they get it inside a Microsoft 365 or Office 365 suite. The feature table puts Microsoft 365 Business Premium and the E3 and E5 suites in the same column as Plan 2 for archiving, holds and DLP, and puts Business Basic, Business Standard and Office 365 E1 alongside Plan 1, with no holds and no DLP. If you are comparing Exchange plans because a suite feels too expensive, the Microsoft 365 E3 and E5 comparison and the Business Premium 300-user cap are the two decisions that usually sit behind it. Endpoint licensing follows a different pattern, set out in the Intune licensing breakdown.
The standalone plans make most sense for frontline or mail-only users, for shared and resource mailboxes, and for organisations that run other workloads elsewhere and only want Microsoft for mail.
Exchange Online Plan 1 vs Plan 2 failure modes
- The inbox that bounces customers. A Plan 1 user who reaches 50 GB triggers Prohibit Send/Receive, and senders get a non-delivery report. The archiving add-on does not fix this because it does not enlarge the primary mailbox.
- The hold you cannot place. A legal request arrives for a Plan 1 mailbox. Litigation Hold is not available on Plan 1, so you need Plan 2 or the add-on assigned before the hold can be set.
- The leaver whose mail vanished. Without inactive mailboxes, removing a licence or deleting the user starts the 30-day soft-delete clock. If nobody exported or held the mailbox in that window, it is gone.
- The journaling workaround. Copying mail into another Exchange Online mailbox with journaling, transport rules or auto-forwarding for archiving purposes is not permitted, according to the limits page. A cheap “archive mailbox” built this way breaks the terms rather than saving money.
- The missing desktop client. Users moved to a standalone plan from a suite lose rights to desktop Outlook unless another licence provides the apps.
- The shared mailbox at 50 GB. It fills quietly because nobody owns it. When it hits the limit, Plan 2 on that one mailbox is the documented route to 100 GB.
What I would do differently
I would not standardise everyone on Plan 2 to avoid the decision. Most users never come near 50 GB, and the features that justify Plan 2 are usually needed for a known group: finance, legal, executives and anyone likely to be named in a dispute.
I would run a mailbox size report before buying anything, sort it by total size, and look only at the top of the list. Users near the Plan 1 ceiling need Plan 2. Users with a large archive and a small inbox can stay on Plan 1 with the archiving add-on.
I would decide the leaver process before the licence. If the organisation needs to keep mail after people leave, inactive mailboxes on Plan 2 are the documented way to do it, and that requirement should drive the choice for every role where it applies.
And I would treat email DLP as a separate question. If the organisation needs it, the honest comparison is often not Exchange Online Plan 1 vs Plan 2 at all, but whether a suite such as Business Premium or E3 already covers it.
Last verified: 31 October 2026.
