# Exchange Online Mailbox Size Limits: 50 GB, 100 GB and Archive Explained > See which Exchange Online mailbox size applies to your licence, how archive and auto-expanding archive add space, and how to check usage and turn archiving on with PowerShell. Source: https://www.epifive.com/blog/exchange-online-mailbox-size-limits-archive · Published 2026-10-25 · EpiFive ## Key takeaways - A user mailbox is 50 GB on Exchange Online Plan 1 and Office 365 E1, 100 GB on Plan 2, Microsoft 365 Business plans and E3 or E5, and 2 GB on Kiosk or F3. - The archive mailbox starts with up to 100 GB of extra space, and Microsoft 365 Business Basic, Standard and Office 365 E1 are listed at 50 GB of archive instead. - Auto-expanding archiving extends the archive to 1.5 TB, is enabled only through Exchange Online PowerShell, and cannot be turned off. - Shared and resource mailboxes are limited to 50 GB without a licence, and a licence is needed to reach 100 GB. - The default archive policy moves items older than two years, so enabling archive alone does not immediately free recent mail. Exchange Online gives a user mailbox 50 GB on Exchange Online Plan 1 and Office 365 E1, 100 GB on Exchange Online Plan 2, Microsoft 365 Business Basic, Standard and Premium and the E3 and E5 plans, and 2 GB on Exchange Online Kiosk and Office 365 F3. If that is not enough, you enable the archive mailbox for up to 100 GB more, and on eligible licences turn on auto-expanding archiving, which grows the archive up to 1.5 TB. ## Who this is for and what you will have at the end This guide is for Microsoft 365 administrators who get "mailbox full" tickets, plan licences, or need to decide between a larger plan, an archive and a cleanup policy. At the end you will have: - The size limit that applies to each mailbox type and licence. - The PowerShell to check how full primary and archive mailboxes are. - The steps to enable archives and auto-expanding archives, with their restrictions. - An understanding of what the default policy moves and when. ## Mailbox size limits by licence Microsoft's Exchange Online limits page states that the mailbox type and the user's subscription licence determine the storage available, and that administrators can reduce maximum mailbox sizes per user or globally. ### Microsoft 365 and Office 365 plans | Mailbox type | Business Basic and Standard | Business Premium | Microsoft 365 E3 or E5 | Office 365 E1 | Office 365 E3 or E5 | Office 365 F3 | | --- | --- | --- | --- | --- | --- | --- | | User mailbox | 100 GB | 100 GB | 100 GB | 50 GB | 100 GB | 2 GB | | Archive mailbox | 50 GB | 1.5 TB | 1.5 TB | 50 GB | 1.5 TB | Not available | | Shared mailbox | 50 GB | 50 GB | 50 or 100 GB | 50 GB | 50 or 100 GB | 50 GB | | Resource mailbox | 50 GB | 50 GB | 50 GB | 50 GB | 50 GB | 50 GB | | Group mailbox | 50 GB | 50 GB | 50 GB | 50 GB | 50 GB | 50 GB | Where the table shows a 1.5 TB archive, Microsoft's footnote explains that each user initially receives 100 GB of storage in the archive mailbox, and that additional storage is added only when auto-expanding archiving is turned on. ### Standalone Exchange Online plans | Mailbox type | Plan 1 | Plan 2 | Kiosk | | --- | --- | --- | --- | | User mailbox | 50 GB | 100 GB | 2 GB | | Archive mailbox | 50 GB | 1.5 TB (100 GB initially) | Not available | | Shared mailbox | 50 GB | 100 GB | 50 GB | | Resource mailbox | 50 GB | 100 GB | 50 GB | | Public folder mailbox | 50 GB | 100 GB | Not available | | Group mailbox | 50 GB | 50 GB | 50 GB | Archive mailboxes are not included in Exchange Online Kiosk. They can be bought as an add-on through Exchange Online Archiving, and an Exchange Online Plan 1 licence with the Exchange Online Archiving add-on also supports auto-expanding archiving up to 1.5 TB. ### Notes that catch administrators out - A shared mailbox does not need its own licence, but without one it is limited to 50 GB. To raise it to 100 GB, the mailbox needs a plan that allows it, such as Exchange Online Plan 2, and a user accessing it needs an Exchange Online licence. - Placing a shared mailbox on litigation hold needs an Exchange Online Plan 2 licence, or Plan 1 with Exchange Online Archiving. Features such as Microsoft Defender for Office 365, eDiscovery (Premium) and retention policies require the shared mailbox to be licensed for them. - Resource mailboxes (rooms and equipment) do not need a licence, and are limited to 50 GB without one. - Public folder mailboxes in Exchange Online: you are limited to 1,000 public folder mailboxes. The default individual public folder size limit is 2 GB. - Archive mailboxes may only archive mail for a single user or entity for which a licence has been applied. Copying mail from many users to one mailbox through journaling, transport rules or auto-forwarding to archive it is not permitted. ## Recoverable Items quotas Deleted items go to the Recoverable Items folder, which has its own quota. In the primary mailbox it is 30 GB, or 100 GB when the mailbox is on hold. When a mailbox is placed on hold and archiving is enabled, quotas are adjusted: for a mailbox on hold or assigned a retention policy, enabling the archive raises the Recoverable Items quota from 100 GB to 105 GB and the warning quota from 90 GB to 95 GB. For how holds relate to retention, see [litigation hold vs retention policy in Exchange](https://www.epifive.com/blog/litigation-hold-vs-retention-policy-exchange). ## Step 1: Check how full mailboxes are Connect to Exchange Online PowerShell, then check the primary mailbox: ```powershell Get-MailboxStatistics -Identity belindan@contoso.com | Format-List DisplayName,TotalItemSize,ItemCount ``` Microsoft recommends `Get-EXOMailboxStatistics` instead in Exchange Online PowerShell. Use the `-Archive` switch to see the archive mailbox that belongs to the user: ```powershell Get-MailboxStatistics -Identity belindan@contoso.com -Archive | Format-List DisplayName,TotalItemSize,ItemCount ``` Compare the primary mailbox size with the limit for the user's licence in the tables above. The archive size matters as much as the primary size, because the primary can only offload to the archive while the archive has space. ## Step 2: Enable the archive mailbox An archive mailbox, also called In-Place Archiving, is an additional mailbox associated with the user's primary mailbox. Users can reach it in Outlook and Outlook on the web. You need the Mail Recipients role in Exchange Online to enable archives. By default it is held by the Recipient Management and Organization Management role groups. ### In the Exchange admin center 1. Open the Exchange admin center and go to **Recipients** > **Mailboxes**. 2. Select the user. 3. In the flyout, select **Others**, and under **Mailbox archive** select **Manage mailbox archive**. 4. Turn on **Mailbox archive** and select **Save**. The **Archive status** column shows **Active** when it has been created, after a refresh. ### With PowerShell For one user: ```powershell Enable-Mailbox -Identity belindan@contoso.com -Archive ``` For all user mailboxes that do not have an archive and have not had one disabled: ```powershell Get-Mailbox -Filter {ArchiveGuid -Eq "00000000-0000-0000-0000-000000000000" -AND DisabledArchiveGuid -Eq "00000000-0000-0000-0000-000000000000" -AND RecipientTypeDetails -Eq "UserMailbox"} | Enable-Mailbox -Archive ``` If an archive was disabled more than 30 days ago, the command fails with a `MissingDisconnectReceiptsException` error. Microsoft's fix is to run `Set-Mailbox` for that mailbox with `-RemoveDisabledArchive`, then run the enable command again. ### Auto-enable on a full mailbox You can have Exchange Online provision an archive automatically when a primary mailbox reaches 90% of its quota: ```powershell Set-OrganizationConfig -AutoEnableArchiveMailbox $true ``` An archive is created automatically only if the mailbox is a user or shared mailbox in Exchange Online, archiving is included in the assigned licence, and the mailbox is not synchronized from on-premises. ### What actually moves When you enable the archive, items older than the archive policy in the assigned retention policy are moved to the archive. The default archive policy in the default retention policy that Exchange Online assigns moves items two years after they were delivered or created. It also moves items 14 days or older from the primary Recoverable Items folder to the archive's Recoverable Items folder. Note that, if you have created a retention policy in Exchange Online, messages are moved automatically only if the primary mailbox is larger than 10 MB. If you disable an archive, items stay in the primary mailbox, and you can reconnect the archive within 30 days with its contents restored. After 30 days the contents are permanently deleted. ## Step 3: Enable auto-expanding archiving Without auto-expanding archiving the archive is capped at its initial quota. With it, Microsoft Purview periodically checks the archive size and adds storage until the archive reaches 1.5 TB. ### Know the restrictions first - It cannot be turned off after you enable it, for the organization or for a user. - Administrators cannot adjust the quota. - It prevents recovering or restoring an inactive mailbox. - The archive must already be enabled. - You cannot use the Exchange admin center or the Purview portal. You must use Exchange Online PowerShell. - It is supported for mailboxes used by individual users or shared mailboxes with a growth rate that does not exceed 1 GB per day. - After you enable it, the archive converts to an auto-expanding archive when it reaches 90 GB including Recoverable Items, and the extra storage can take up to 30 days to be provisioned. - After an auto-expanded storage area exists, users cannot delete folders in the archive, and cannot use Recover Deleted Items for items in it. ### Turn it on For everyone: ```powershell Set-OrganizationConfig -AutoExpandingArchive ``` For one user (the archive must already be enabled): ```powershell Enable-Mailbox belindan@contoso.com -AutoExpandingArchive ``` When you enable it for one user whose mailbox is on hold or has a retention policy, the archive quota rises from 100 GB to 110 GB, and the warning quota from 90 GB to 100 GB, to bridge the gap until the extra storage is provisioned. The organization-wide command does not add that extra space. Verify: ```powershell Get-OrganizationConfig | FL AutoExpandingArchiveEnabled Get-Mailbox belindan@contoso.com | FL AutoExpandingArchiveEnabled ``` A value of `True` means it is enabled. Setting it for the whole organization does not change the property on individual mailboxes. ### Larger limit for E5 licences Microsoft states that it is raising the maximum auto-expanding archive capacity for eligible mailboxes from 1.5 TB to 3 TB, with rollout beginning in mid-October 2026 and expected to complete by late October. It applies to licences such as Office 365 E5, A5 and G5, Microsoft 365 E5, A5 and G5, and the Microsoft 365 Purview Suite. For all other licences the 1.5 TB limit stays. For E5 licences, Records Management must be selected in the user's licence settings. Check the documentation again before you rely on the 3 TB figure, because rollout dates can move. ## Step 4: Know about auto-archiving Auto-archiving is a separate, threshold-based feature. When a primary mailbox exceeds 96% of its quota by default, and the archive is provisioned and has space, the Managed Folder Assistant moves the oldest items first. Items tagged Never Move to Archive, and items received less than 60 days ago, are excluded. Microsoft's page describes the feature as being in preview with availability on the Microsoft 365 Roadmap, so confirm it is available in your tenant. It does not create archives or turn on auto-expanding archiving, and if the main archive is full without auto-expanding archiving, it moves nothing. The threshold is set organization-wide with `Set-OrganizationConfig -AutoArchivingThresholdPercentage`, with a valid range of 80 to 100, and 100 turns the feature off for the tenant. A user can be excluded with `Set-Mailbox -AutoArchivingEnabled $false`. ## Troubleshooting | Symptom | Likely cause | Fix | | --- | --- | --- | | Mailbox is full but an archive exists | Items are younger than two years, so the default policy has not moved them | Customize the archive policy, or rely on auto-archiving where available | | Archive is full too | Archive limited to its initial quota | Enable auto-expanding archiving if the licence allows it | | Cannot enable auto-expanding archive in the admin center | It is PowerShell only | Use `Enable-Mailbox -AutoExpandingArchive` | | Enable archive fails with `MissingDisconnectReceiptsException` | Archive disabled more than 30 days ago | `Set-Mailbox -RemoveDisabledArchive`, then enable again | | No archive option for a user | Kiosk or F3 licence | Add the Exchange Online Archiving add-on | | Shared mailbox stuck at 50 GB | No licence on the mailbox | Assign a plan that raises it to 100 GB | | Archive not created automatically | Mailbox synchronized from on-premises, or licence has no archiving | Enable it manually | ## Summary checklist - Confirm the licence of the mailbox and look up its limit in the tables. - Check primary and archive sizes with `Get-MailboxStatistics`, using `-Archive` for the archive. - Enable the archive, and decide whether you want automatic provisioning at 90%. - Enable auto-expanding archiving only where users need it, because it cannot be reversed. - Use retention policies to delete content that has no business value, so mailboxes do not grow without bound. - Review shared mailboxes and give licences where they need more than 50 GB or holds. ## References - [Exchange Online limits (Microsoft Learn)](https://learn.microsoft.com/en-us/office365/servicedescriptions/exchange-online-service-description/exchange-online-limits) - [Enable archive mailboxes (Microsoft Learn)](https://learn.microsoft.com/en-us/purview/enable-archive-mailboxes) - [Learn about archive mailboxes (Microsoft Learn)](https://learn.microsoft.com/en-us/purview/archive-mailboxes) - [Learn about auto-expanding archiving (Microsoft Learn)](https://learn.microsoft.com/en-us/purview/autoexpanding-archiving) - [Enable auto-expanding archiving (Microsoft Learn)](https://learn.microsoft.com/en-us/purview/enable-autoexpanding-archiving) - [Auto-archiving in Exchange Online (Microsoft Learn)](https://learn.microsoft.com/en-us/exchange/security-and-compliance/messaging-records-management/auto-archiving) - [Get-MailboxStatistics (Microsoft Learn)](https://learn.microsoft.com/en-us/powershell/module/exchangepowershell/get-mailboxstatistics) ## Frequently asked questions ### How big can an Exchange Online mailbox be? It depends on the licence. Exchange Online Plan 1 and Office 365 E1 give a user mailbox 50 GB, while Exchange Online Plan 2, Microsoft 365 Business Basic, Standard and Premium, and E3 or E5 plans give 100 GB. Exchange Online Kiosk and Office 365 F3 give 2 GB. ### Does a shared mailbox need a licence? A shared mailbox does not need a licence to exist, but without one it is limited to 50 GB. To go to 100 GB it must be assigned an Exchange Online Plan 2 licence, and Microsoft's table lists an E3 or E5 licence as the way to get 100 GB on Microsoft 365 plans. Features such as litigation hold also need a suitable licence on the shared mailbox. ### How do I get more than 100 GB of mailbox space? Enable the archive mailbox, which gives up to 100 GB of extra storage, then turn on auto-expanding archiving with Exchange Online PowerShell where your licence supports it. Auto-expanding archiving grows the archive up to 1.5 TB, and cannot be turned off once it is on. ### Why did my mailbox fill up when I have an archive? The default archive policy moves items two years or older, so recent mail stays in the primary mailbox. If the archive is not enabled, or the archive itself is full without auto-expanding archiving, nothing more moves. Enable the archive, and check both mailboxes with Get-MailboxStatistics.