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How to raise the Outlook attachment limit to 150 MB in Microsoft 365
Raise a Microsoft 365 mailbox's message size limits in the Exchange admin center so users can send and receive attachments up to 150 MB in Outlook and Outlook on the web.
By Nur Islam- 2:02 video
- 4 steps
- 15.1K views
Jump to a step (4)
Staff trying to email large files get the error that the file is bigger than the server allows. Microsoft 365 mailboxes start with lower default limits, and many small business admins do not know they can raise them per mailbox.
Message size limits are set per mailbox in the Exchange admin center. You can raise both the send and receive limits to a maximum of 153600 KB, which is 150 MB. The change applies to the Outlook app and Outlook on the web, but it can take a while to take effect.
What you need
- A Microsoft 365 business subscription with Exchange Online
- A Microsoft 365 admin account with access to the Exchange admin center
- The mailbox you want to change
Step by step
0 of 4 done-
01
Open the Exchange admin center
In the Microsoft 365 admin center, click Show all in the left menu and select Exchange. You can also go straight to
admin.exchange.microsoft.com. -
02
Open the mailbox
Go to Recipients > Mailboxes. Click the name of the user whose limit you want to raise, then select the Mailbox tab in the panel that opens.
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03
Change the message size restriction
Click Manage message size restrictions. Enter the new limits in KB in both boxes: the sent message limit and the received message limit. The maximum is
153600KB (150 MB). Click Save; you should see a settings updated message. -
04
Wait and test
Microsoft says changes can take a few minutes, but in the video it took around 30 minutes. Then attach the large file again. The 107 MB file that failed before attaches without the error, in Outlook and in Outlook on the web.
Tips and common problems
- Limits are entered in KB, not MB. 150 MB is 153600 KB.
- The change is per mailbox. Repeat it for each user who needs to send large files.
- Allow up to 30 minutes before testing, even though the admin center says about 5 minutes.
- A higher limit on your side does not change the recipient's server. Their mailbox may still reject large messages.
Questions
What is the maximum attachment size in Outlook for Microsoft 365?
An admin can raise a mailbox's send and receive limits to 150 MB (153600 KB) in the Exchange admin center. The default limits are lower.
Why does Outlook say the file is bigger than the server allows?
The file is larger than the message size limit set on your mailbox. An admin can raise it under Recipients > Mailboxes > Mailbox > Manage message size restrictions.
Do I need to be an admin to increase the attachment limit?
Yes. The limit is a mailbox setting in the Exchange admin center, so it needs an Exchange or global admin account.
