Outlook attachment size limit: 20, 25 or 35 MB?
Short answer
Outlook.com allows 25 MB per email, the Outlook desktop app with a personal account 20 MB, and Microsoft 365 work accounts 35 MB by default (up to 150 MB if your admin raises it). Encoding means only about two-thirds of that is real file.
| Account | Limit |
|---|---|
| Outlook.com (web) | 25 MB per email, message included |
| Outlook desktop app, personal accounts | 20 MB |
| Microsoft 365 work accounts | 35 MB by default, up to 150 MB if your admin raises it |
| OneDrive links from Outlook.com | Up to 2 GB per linked file |
Why the number you see isn't the number you get
Email turns attachments into text before sending them (base64 encoding), which makes them about a third bigger. A 20 MB file is roughly 27 MB once it's in an email, so it fails against a 25 MB limit. And even if Outlook sends it, the recipient's mail server can still bounce it: many company mail servers accept 10–25 MB at most.
What Outlook does with bigger files
Outlook offers to upload the file to OneDrive and insert a link. That works, with the usual catches: the file counts against your OneDrive storage (5 GB on a free Microsoft account), you need to get the sharing permissions right, and on a work account your company may block links to people outside the organization.
Send a link that works anywhere
Upload the file to Send Shed's Quick Share (free, no account, up to 3 GB per file) and paste the link into your email. No storage quota, no permissions to set, and the recipient's mail server never sees the file. Add a password or a one-download limit for anything personal, or use Encrypted Share for tax documents and contracts.
Quick answers
What is the Outlook attachment size limit?
Outlook.com allows 25 MB per email, including the message and attachments. The Outlook desktop app with a personal account such as Outlook.com or Gmail allows 20 MB. Work accounts on Microsoft 365 default to 35 MB, which administrators can raise to 150 MB.
Why does Outlook say my 20 MB file is too large?
Email encodes attachments in a way that makes them about a third larger, so a 20 MB file becomes roughly 27 MB in transit. The recipient's mail server may also have a lower limit than yours.
How do I send a file larger than 25 MB in Outlook?
Outlook can attach it as a OneDrive link instead (Outlook.com allows linked files up to 2 GB), or you can upload it to a file-sharing service and paste the link into the email.
Too big? Send it here instead
Upload it to Quick Share — up to 3 GB per file, free, no account — and paste the link wherever you were trying to attach it. Unused links delete themselves.
Send it with Quick Share Send it encrypted