In short
Exchange Online Archiving gives each licensed user an archive mailbox with up to 100 GB of extra storage, which auto-expanding archiving can grow to 1.5 TB (3 TB for eligible E5-type licences from October 2026). Many plans include it; others can add the EOA add-on. It stays inside your tenant, so it is not a separate journaled copy of your mail.
Get a quote for Microsoft 365 email archiving
Tell us roughly how many users or sites you have and we will reply by email with options and a quote.
What Exchange Online Archiving is
The name covers two related things. The archive mailbox (sometimes called an In-Place Archive) is a second mailbox attached to a user's primary mailbox, which users and archive policies move older mail into. Exchange Online Archiving (EOA) is also the name of Microsoft's product that provides that archive, either included in a Microsoft 365 plan or bought as an add-on.
Microsoft's service description calls it "a Microsoft 365 cloud-based, enterprise-class archiving solution" that "assists organizations with archiving, compliance, regulatory, and Microsoft Purview eDiscovery challenges." In practice it does three main jobs: it frees space in primary mailboxes, it lets retention policies and holds reach older mail, and it keeps that mail searchable with Microsoft Purview eDiscovery.
It is not the same as Outlook's Archive button, which just moves a message to an Archive folder in the primary mailbox. Our what is email archiving? guide explains the difference.
Archive mailbox size and auto-expanding archiving
The numbers, from Microsoft's current documentation:
- 100 GB of extra storage when an archive mailbox is enabled, with a warning at 90 GB
- If the mailbox has a hold or retention policy and auto-expanding archiving is on, the quota rises to 110 GB before expansion starts
- Auto-expanding archiving then adds space in stages up to 1.5 TB; new space can take up to 30 days to provision
- Microsoft is raising the maximum to 3 TB for mailboxes with eligible licences, such as Microsoft 365 E5 and Office 365 E5 and qualifying Purview suites, with rollout from mid-October 2026; other licences stay at 1.5 TB
- Auto-expanding archives support a growth rate of no more than 1 GB a day
There are side effects worth telling users about. Folders may be moved or split into dated subfolders in the expanded storage. Once an expanded area exists, users cannot delete folders from the archive, and they cannot use Recover Deleted Items for items in it. Holds, retention policies and eDiscovery searches do cover the expanded storage.
Which plans include archiving and where the add-on fits
Microsoft's Exchange Online Archiving service description sets out which plans already include archiving and which can take EOA as an add-on. At the time of writing:
| Already include archiving | Can add Exchange Online Archiving |
|---|---|
| Exchange Online Plan 2 | Exchange Online Plan 1 |
| Microsoft 365 Business Premium | Exchange Online Kiosk |
| Microsoft 365 E3 and E5 | Microsoft 365 Business Basic and Business Standard |
| Office 365 E3 and E5 | Office 365 E1, A1 and G1 |
| Office 365 A3 and A5 | Office 365 F3 and Microsoft 365 F3 |
| Microsoft 365 F5 Compliance | - |
On the plans in the right-hand column, Microsoft's service description says the add-on brings auto-expanding archiving and In-Place Hold and Litigation Hold, although new In-Place Holds can no longer be created in Exchange Online. There is also Exchange Online Archiving for Exchange Server, a cloud archive for users whose primary mailboxes stay on a supported on-premises Exchange Server, which needs an Exchange hybrid deployment. Microsoft now favours retention policies and eDiscovery holds over the older hold types; see our guide to legal hold.
Plan contents change, so check your own subscriptions. Buying or changing Microsoft licences is handled by Forever Group's Microsoft licensing team.
Not sure which plan fits? Ask us
Tell us what you need and we will recommend the right plan for your organisation, with a quote.
What Exchange Online Archiving does not do
EOA is a good mailbox management and retention tool. It is not designed to be an independent record, and Microsoft's own terms make some limits clear:
- It lives in your tenant. The archive is part of the same Microsoft 365 environment, under the same administrators and the same retention settings. A mistaken retention policy or a compromised admin account affects it too.
- It is not a journaled copy. Mail reaches the archive because a user or an archive policy moves it there, not because a copy was taken when it was sent or received. Without retention or a hold, users can still delete it.
- One user per archive. Microsoft says an archive mailbox can only hold mail for the single licensed user. Using journaling, transport rules or auto-forwarding to copy messages into an archive mailbox for archiving is not permitted.
- Leavers need planning. When an account is deleted, the mailbox and its archive are only kept as an inactive mailbox if a hold or retention policy applied before deletion; otherwise the data is removed after 30 days. See former employee mailboxes.
- It is not a backup. For restoring mailboxes, OneDrive and SharePoint after deletion or ransomware, see our Cloud Security site on Microsoft 365 backup.
Exchange Online Archiving vs a journaling archive
The two are often used together, because they solve different problems.
| Exchange Online Archiving | Journaling archive (NinjaOne Archiver) | |
|---|---|---|
| Main purpose | More mailbox space; retention and holds in place | An independent, unaltered record of all mail |
| How mail gets there | Moved by users or archive policies | Journaled as it is sent and received |
| Where it sits | Inside your Microsoft 365 tenant | In NinjaOne's cloud, outside your tenant |
| Who can change it | Users and tenant admins, within retention rules | Held apart from the mailbox with audit trails; optional WORM setting |
| Search | Microsoft Purview eDiscovery | NinjaOne eDiscovery with saved searches, tags and alerts |
| Access for compliance staff | Purview roles | Compliance and Review Officer, Data Protection Officer and Reviewer roles; the IT Admin role has no compliance access |
| Leavers | Inactive mailbox if held first | Archived mail stays available after the account goes |
| Backup included | No | SaaS Backup Standard in the Archiver bundles |
Because Exchange Online cannot journal to its own mailboxes, a journaling archive is by definition outside the tenant. The Exchange Online journaling page explains how NinjaOne Archiver receives the journal reports.
Is Microsoft 365 email archiving the right fit for you?
We will check it against your systems and requirements and recommend the right option.
Using both together
A common, sensible pattern:
- Archive mailboxes keep primary mailboxes a manageable size and give users their older mail in Outlook.
- Microsoft 365 retention handles SharePoint, OneDrive and Teams content in place.
- NinjaOne Archiver keeps the independent, journaled record of email, with its own retention by department or user, legal hold and reviewer access, plus backup for the tenant.
That way users keep the convenience they are used to, and your compliance, HR and legal staff have one controlled place to search, including former employees' mail. The Office 365 email archiving overview compares the native options in more detail.
How Forever Systems helps
We supply NinjaOne SaaS Backup with Archiver and help you put it alongside what Microsoft already gives you. We can review how archive mailboxes, retention policies and holds are set up in your tenant today, suggest where a journaling archive adds something and where it does not, and help set it up. If the right answer is a Microsoft licence change, Forever Group's Microsoft team can help with that.
The archive is priced by bundle, user count and term, so ask us for a quote. Contact us.
How Forever Systems helps with email archiving
We are an independent UK IT and cyber security provider. We supply NinjaOne SaaS Backup with Archiver for organisations on Microsoft 365 or Google Workspace, and help you get the archive set up, the policies right and the people who need it confident using it.
- Scoping: we look at your mailboxes, leavers, legacy archives and record-keeping obligations, and what your Microsoft 365 or Google Workspace plan already includes, before suggesting anything new
- Set-up: we can configure journaling for Exchange Online or Google Workspace, connect the archive and check that mail is arriving
- Retention and legal hold: we help you turn your email retention policy into archive rules, and show your compliance or HR lead how to search, hold and export
- Leavers and legacy archives: we can help you plan how former employees' mail and older archives are brought across, with the approach confirmed at quote
- Backup alongside the archive: the same NinjaOne per-user licence also covers backup of your Microsoft 365 or Google Workspace data, so recovery and record-keeping are planned together
We work with businesses, schools, charities and public sector organisations. If you also need wider protection, see our independent cloud security guides.
Frequently asked questions
What is Exchange Online Archiving?
Exchange Online Archiving is Microsoft's archive mailbox service for Exchange Online and on-premises Exchange Server users. It gives each licensed user an archive mailbox with extra storage, retention and hold features, searchable with Microsoft Purview eDiscovery. Some plans include it; others can buy it as an add-on.
How big can an Exchange Online archive mailbox get?
An archive mailbox starts with up to 100 GB. With auto-expanding archiving it can grow to 1.5 TB, and Microsoft is raising that to 3 TB for eligible E5-type licences, with rollout from mid-October 2026. Growth is limited to 1 GB a day.
Does Microsoft 365 Business Premium include Exchange Online Archiving?
Microsoft's service description lists Microsoft 365 Business Premium among the plans that already include archiving, so it does not need the add-on. Business Basic and Business Standard can add it. Check your own subscriptions, as plan contents change.
Is Exchange Online Archiving a backup?
No. It keeps older mail in an archive mailbox inside your tenant, under the same admins and retention settings. It does not give you an independent copy you can restore from after deletion or ransomware.
Can I journal mail into an Exchange Online archive mailbox?
No. Microsoft does not permit journaling, transport rules or auto-forwarding to copy messages into an archive mailbox, and an Exchange Online mailbox cannot be a journaling mailbox. Journaled mail has to go to an outside archive.
Does Exchange Online Archiving work with on-premises Exchange?
Yes. Exchange Online Archiving for Exchange Server gives a cloud archive to users whose primary mailboxes are on a supported on-premises Exchange Server, but it requires an Exchange hybrid deployment.
Still have a question about Microsoft 365 email archiving?
Ask us and a member of our team will reply by email.