Sending a file that is too large to email

You attach the file, click send, and one of two things happens: Outlook refuses to attach it in the first place, or the message comes bouncing back a few minutes later saying it couldn't be delivered because it was too big. Nothing is broken and you haven't done anything wrong — you've run into a limit that every email system in the world has, including the one at the other end.

Why email can't carry large files

Email still works the way it always did: an attachment is copied into the message itself and pushed through every mail server between you and your recipient. Each of those systems gets a vote. Your organization sets a maximum message size, the recipient's organization sets its own, and the smaller of the two decides. That's why a file can leave your outbox perfectly happily and still be refused at the other end — the message isn't delivered, and you get a non-delivery report, the bounce-back that lands in your inbox telling you it was too large.

Classic Outlook for Windows may stop you before the message is ever sent, with an error that quietly gives away the correct answer: "The file you're attaching is bigger than the server allows. Try putting the file in a shared location and sending a link instead." That really is the fix.

How big is too big?

There's no single number, and any article that gives you one is guessing. The maximum message size is set by your organization, and administrators can set it anywhere from 1 MB to 150 MB. Microsoft's default for a Microsoft 365 mailbox is 35 MB for messages you send and 36 MB for messages you receive — a starting point, not a universal rule. It can even be set differently for individual people in the same office.

Two things make the practical limit smaller than that number suggests:

• Files get bigger in transit. A message leaving Microsoft's datacenters is re-encoded on the way out, which adds roughly a third to its size. A file that looks comfortably under the limit on your screen can be over it by the time it's actually moving.
• The app you send from has its own ceiling. Outlook in a web browser deliberately holds you to 25% below whatever your organization has configured — if the limit is 100 MB, the browser stops you at 75 MB. The Outlook apps for iPhone and Android stop at 33 MB regardless of what your organization allows. Whichever is lower, your organization's setting or your app's, is the one that applies.

And none of that accounts for the recipient. Their organization enforces its own limit on incoming mail, and some cap the size of individual attachments as a matter of policy. You have no way to know their number in advance, which is the real reason a link beats an attachment for anything sizable leaving the office.

Send a link instead

A link solves all of this at once. The email itself stays a few kilobytes, so no size limit along the route can turn it away. The file stays in one place — your OneDrive — so your recipient opens the current version rather than a copy that started going out of date the moment you hit send. And because you're granting access rather than handing over a copy, you can change or remove that access later.

Size stops being the issue, too: a single file in OneDrive or SharePoint can be up to 250 GB, and a OneDrive file shared as a link from Outlook in a browser can be up to 2 GB.

Option 1: Share it while you're writing the email

1. Make sure the file is saved in your OneDrive folder — in File Explorer, OneDrive appears in the column down the left-hand side, and anything saved there is already in the cloud.
2. Start a new message and use the attach-file command on the ribbon. The exact wording differs between classic Outlook for Windows, the new Outlook and Outlook in a browser, but it sits in the same place in all of them.
3. Pick the file from your OneDrive. If you choose a file from your computer instead, Outlook offers to upload it to OneDrive and send a link rather than a copy — take that option.
4. Set who's allowed to open it, and whether they can edit or only view, before you send. See choosing who can open the link below.
5. Send.

Option 2: Share from OneDrive and paste the link

Use this when the file is very large, when it already lives in the cloud, or when you want to check the sharing settings properly before committing.

1. Sign in to OneDrive in a web browser with your work account, or find the file in your OneDrive folder in File Explorer.
2. If the file isn't there yet, upload it. A large file takes a while — leave the browser tab open until it finishes.
3. Select the file and choose the option to share it.
4. Choose who the link is for, and whether they can edit or only view.
5. Copy the link and paste it into your email with a line explaining what it is.

If the file already lives in a Teams channel or a SharePoint site your team shares, share it from there instead of making a second copy in your own OneDrive. Same idea, and everyone stays on one version of the file.

Choosing who can open the link

This is the one decision worth slowing down for, and it takes about five seconds. OneDrive, SharePoint and Outlook all offer a version of the same four choices — the wording varies a little between them, the meaning doesn't.

• Specific people — only the people you name can open it, and they sign in as themselves to do it. The most restrictive option, and the right default for anything that isn't already public.
• People in your organization — anyone inside your company who has the link. Fine for internal material, but it can be forwarded internally.
• People who already have access — changes no permissions at all. Useful when everyone involved can already open the file.
• Anyone with the link — works for whoever ends up holding the link, forwarded or not, inside the company or outside it. The loosest setting, and plenty of organizations switch it off entirely. If you don't see it, that's why.

Separately, you choose whether recipients can edit the file or only view it. If they only need to read it, choose view — one click, and an accidental edit can't land in your copy.

Sending something confidential

For anything sensitive, restrict the link to specific people. A link that works for "anyone" is only as protected as the least careful inbox it eventually lands in.

• Name your recipients explicitly instead of using a general-purpose link.
• Give view-only access unless they genuinely need to change the file.
• Send the link to a named person rather than dropping it in a group chat or shared mailbox, where the audience is wider than you think.
• When the work is finished, remove the sharing. The file is still yours, and access can be switched off at any point.

Does zipping the file help?

Sometimes. Zipping is genuinely useful for bundling: if you're sending twenty small files, one zip folder is a single item to attach and a single item to save, and nothing gets missed.

What it isn't is a way around a size limit. How much a zip file shrinks depends entirely on what's inside it — some files compress a lot, others barely at all, and you can't tell in advance. If your file is well over the limit, zipping won't close the gap, and splitting it into multiple zip parts just hands the problem to your recipient, who now has to put it back together correctly. Send a link instead.

If the recipient can't open the link

This comes up most often with people outside your organization. External sharing is governed by settings your organization controls, and they're frequently kept deliberately tight. If your recipient is asked to sign in and can't, or is told they don't have permission, the file itself is fine — the permission on the link just isn't right for them.

Check two things first. Make sure you sent the link to the same email address the recipient actually uses, because a link restricted to specific people is tied to the exact address you named. And make sure the file is still there — a link points at the live file, so if the file has been deleted the link stops working. If a file has gone missing, you can often get it back yourself: see restoring deleted files in OneDrive and SharePoint. If it still won't open for them, that one's ours to sort out.

If you still can't send the file

Submit a support request or email [email protected], and include as much of this as you can. It's the difference between us fixing it on the first pass and trading messages back and forth:

• What you're trying to send, and roughly how big the file is.
• Who it's going to, and whether they're inside or outside your organization.
• Which app you sent from — classic Outlook for Windows, the new Outlook, Outlook in a web browser, or Outlook on your phone. If you tried more than one, tell us what each of them did.
• The error message, word for word. If you got a bounce-back message, forwarding that to us is better still.
• What you've already tried — a link, zipping the file, sending from a different app.
• The name of your computer, and when this started. Has this file, or a file this size, gone through before?

If you haven't sent us a ticket before, here's how.