Send large files in Outlook

"Bigger than the server allows": what Outlook is telling you

When you attach something too big in classic Outlook for Windows, it shows:

The file you're attaching is bigger than the server allows. Try putting the file in a shared location and sending a link instead.

Microsoft gives two different reasons for that error, depending on your account:

• An internet account (POP3 or IMAP). Classic Outlook itself refuses attachments that add up to more than 20 MB, whether that's one big file or several smaller ones. Microsoft says this default prevents your computer from continually trying to upload very large attachments that most providers would reject anyway.
• A work mailbox. The limit comes from the mail server's maximum send size, which your administrator sets. For Microsoft 365 work mailboxes, Microsoft's default is 35 MB for sending. On an older, on-premises Exchange Server, the default is 10 MB.

That exact wording is classic Outlook's. Whichever Outlook you use, the fix is the one the error suggests: put the file somewhere shared and send a link.

Which Outlook you're using, and its limit

Send a big file from Outlook, step by step

1. Put the file in OneDrive, or in whichever cloud storage you use.
2. Share it so that anyone with the link can open it, and copy the link.
3. In Outlook, start a new message and paste the link into the body where you'd have attached the file. This works the same in new Outlook, classic Outlook and Outlook on the web.
4. Send. The email is a few lines of text, so it's nowhere near any limit.

On your phone: Outlook for iOS and Android attaches files with the paperclip icon on the New mail screen. For a big file, skip that: copy a share link from your storage app instead. Then paste it into a new message in the Outlook app.

A dedicated SendTheStuff upload tool is launching soon for files you'd rather not park in OneDrive at all.

OneDrive: Microsoft's own workaround

Microsoft's advice for big files is to upload them to OneDrive, then "copy the link, and paste it into your email message". In Outlook.com, OneDrive links don't count toward the email size limit, and a linked file can be up to 2 GB.

That's a good choice if you already keep the file in OneDrive and want it to stay there. Two catches. The file keeps using your OneDrive space until you delete it, so tidy up once the recipient has it. And a file bigger than 2 GB needs a different service.

Raising classic Outlook's limit, and why it rarely helps

Microsoft documents a registry value, MaximumAttachmentSize, that changes classic Outlook's 20 MB default for internet accounts. It only moves Outlook's own check. Your email provider's server still has its limit, and so does the recipient's. So a bigger attachment often just fails later, after you've waited for it to upload.

Microsoft also tells you to back up the registry before editing it. For most people, a link is quicker and safer.

Sending to people outside your organization

At work, attachments to outside addresses can run into the company's own rules as well as the size limit. Check your company's policy before sending work files through any outside service.

Many companies let you share a OneDrive file with outside people, but an administrator can switch that off. If a link won't open for someone outside the company, that's usually why, and only IT can change it.

When it doesn't work

• The error appears for a file under the limit you expected. Check the total of all attachments, not just the newest one, and remember that at work the limit is whatever your administrator set. Send a link either way.
• You raised the registry limit and the email still bounces. The server's limit, or the recipient's, is lower. Send a link.
• The recipient can't open your OneDrive link. Check the file's sharing settings in OneDrive. A link limited to specific people makes everyone else sign in or verify their email first.
• Outlook attached a copy instead of a link. When you add a cloud file through the attach menu, Outlook can offer to attach it as a copy, which counts toward the limit. Paste the link into the body instead.