What are the Limits in Exchange Online?
Microsoft publishes the Exchange Online limits by plan. The table lists the main mailbox size limits.
| Mailbox | Plan | Size |
|---|---|---|
| User | Exchange Online Plan 1 and Office 365 E1 | 50 GB |
| User | Exchange Online Plan 2, Microsoft 365 and Office 365 E3 and E5, Business Basic, Standard and Premium | 100 GB |
| User | Kiosk and Office 365 F3 | 2 GB |
| Archive | Plan 2 and E3 or E5 suites | 100 GB at start, up to 1.5 TB with auto expanding archiving |
| Shared | Without a license | 50 GB |
| Shared | With Plan 2 or E3 or E5 license | 100 GB |
Mailbox size limits shift over time, so check the Microsoft page before you plan a migration. Our Exchange Online migration checklist lists the size checks to make first.
What are the Message Size Limits?
| Item | Exchange Online | Exchange Server default |
|---|---|---|
| Message in Outlook | 150 MB | 10 MB |
| Message in Outlook on the web | 112 MB | 10 MB |
| Message in Outlook for iOS and Android | 33 MB | 25 MB |
| Files per message | 250 | 1,024 |
Microsoft states that admins can set a custom limit between 1 MB and 150 MB in Exchange Online, with a default of 35 MB for sending and 36 MB for receiving. Email clients can enforce lower limits.
How do Mailbox Quotas Work?
Exchange sets a mailbox size limit with three quotas. The warning quota sends a message to the owner. The prohibit send quota blocks sending, and the prohibit send and receive quota blocks both.
- IssueWarningQuota. The warning level.
- ProhibitSendQuota. Sending stops here.
- ProhibitSendReceiveQuota. Sending and receiving stop here.
Microsoft states that you can lower or raise quotas in Exchange Online, but you cannot exceed the maximum that the license permits.
How do You Edit a Quota in Exchange Server?
Quotas sit on the mailbox database and apply to every mailbox in it. Microsoft documents the Set-Mailbox command for one mailbox. Set UseDatabaseQuotaDefaults to false, or the database values win.
Set-Mailbox -Identity "Joe Healy" -UseDatabaseQuotaDefaults $false -IssueWarningQuota 24.5GB -ProhibitSendQuota 24.75GB -ProhibitSendReceiveQuota 25GBThe warning quota must be at or below the other two. Check the result with Get-Mailbox and Format-List.
What if a Mailbox is Full?
- Empty Deleted Items and Recoverable Items.
- Enable the archive mailbox if your license includes it.
- Export old mail to a PST file and remove it from the mailbox.
- Move the mailbox to a plan with a higher limit.
The Exchange Export Tool exports mailboxes to PST. Our PST file guide explains the 50 GB limit of the PST format, and the guide to split a large PST suits oversized exports.
Frequently Asked Questions
How Big is an Exchange Online Mailbox?
It depends on the plan. Plan 1 and Office 365 E1 give 50 GB. Plan 2 and the E3 and E5 plans give 100 GB.
How Big is a Shared Mailbox?
Microsoft lists 50 GB without a license. It rises to 100 GB with a Plan 2 or E3 or E5 license.
What is the Largest Message in Exchange Online?
Outlook sends messages up to 150 MB. Outlook on the web accepts 112 MB.
What is the Default Message Size in Exchange Server?
Microsoft lists 10 MB for Outlook and Outlook on the web. An admin can adjust it.
Can You Raise a Quota Past the License Limit?
No. Microsoft states that you cannot exceed the maximum that the license permits.
Which Command Edits a Mailbox Quota?
Use Set-Mailbox with the three quota parameters and set UseDatabaseQuotaDefaults to false.
How do You Free Space in a Full Mailbox?
Empty Deleted Items, use the archive and export old mail to PST.
Author's Verdict
Check the mailbox size limit before you add data, because you cannot raise a quota past the license.
Use the archive and PST export to remain under the limit.
Key Takeaways
- Plan 1 mailboxes store 50 GB and Plan 2 mailboxes store 100 GB.
- Outlook messages reach 150 MB in Exchange Online.
- Quotas never exceed the license maximum.
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