Outlook.com accepts up to 25 MB of attachments per message on personal accounts, all files combined, and lets you share files from OneDrive as a link up to 2 GB each. Microsoft 365 work and school mailboxes run on Exchange Online, where the default is 35 MB per message sent and 36 MB received, and an administrator can set any organization limit between 1 MB and 150 MB. A file over the limit is not silently refused: Outlook offers to upload it to OneDrive and insert a link instead.
Which limit applies to your account?
| Account or client | Send | Notes |
|---|---|---|
| Outlook.com (personal) | 25 MB per message | OneDrive links up to 2 GB per file; limits are lower for non-subscribers |
| Microsoft 365 mailbox (default) | 35 MB sent, 36 MB received | Administrator can set 1 MB to 150 MB organization-wide |
| Outlook desktop (Windows, Mac) | Up to 150 MB per message | Only if the organization limit allows it |
| Outlook on the web | Up to 112 MB per message | Client limit, below the 150 MB maximum |
| Outlook for iOS and Android | 33 MB per message | The lowest client limit |
The figures come from Microsoft's own pages: Sending limits in Outlook.com and the Exchange Online limits service description, both checked on 2026-09-14. Microsoft notes that the message you can actually send or receive also depends on what the recipient's mail system and your email client support, so the smallest limit in the chain wins.
Why does a 20 MB file still bounce?
Email cannot carry raw binary data. Attachments travel as Base64 text, which is about a third larger than the file on disk, and Outlook measures the encoded message, not the size you see in Explorer or the Finder. A 20 MB PDF becomes roughly 27 MB in transit and fails the 25 MB check on Outlook.com. In practice, files up to about 18 MB attach reliably on a 25 MB account, and about 26 MB on a 35 MB Microsoft 365 mailbox.
The recipient's limit matters too. A 30 MB message sent from a Microsoft 365 mailbox with a raised limit still bounces when it reaches a personal Outlook.com or Gmail account capped at 25 MB, and the error arrives after sending, as a non-delivery report.
How do you send a file larger than 25 MB?
Three ways, from least to most control over what the recipient gets.
- Let Outlook use OneDrive. Attach the file as usual. When it is over the limit, Outlook offers to upload it to OneDrive and share a link, up to 2 GB per file. The recipient needs the link permission you choose (anyone, or people in your organization), and the file counts against your OneDrive storage (5 GB on a free Microsoft account, 1 TB with Microsoft 365).
- Compress before attaching. A
.zipshrinks documents, spreadsheets and layered design files. It does almost nothing for photos and video, which are already compressed. - Send a transfer link instead of an attachment. A transfer service uploads the files once and puts a download link in the email, so neither mailbox limit applies. Brault Transfer sends up to 2 GB per transfer on the free plan (5 transfers a month) and up to 250 GB per transfer on Growth, with a branded download page, an expiry you set and an optional password.
For video specifically, the guide on how to send large video files compares the options by file size and quality loss, and how to send large files via email covers the Gmail, Outlook and Apple Mail fallbacks side by side.
What else stops an attachment?
- Blocked file types. Outlook refuses executable and script files such as
.exe,.jsand.bat, and Exchange Online administrators can block more. - Attachment count. Exchange Online also limits how many files a message can carry, separately from the size, so a folder of many small files travels better as one
.zipor one transfer. - Full mailbox. Once a mailbox reaches its storage quota, it stops receiving until space is freed, whatever the attachment size.
- Daily sending limits. Outlook.com allows 5,000 recipients a day for Microsoft 365 subscribers, 500 per message, and lower figures for non-subscribers, so a large send to many people can be refused for reasons unrelated to the file.