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You've attached a file in Outlook, hit send, and moments later it either refuses to attach or bounces straight back with a size error. It's one of the most common frustrations in email: the thing you need to send — a video, a design file, a stack of photos, a database export — is simply too big for the inbox. The good news is that getting a large file to someone through Outlook is easy once you know the options. This guide explains Outlook's real attachment limit, then walks through three reliable ways to send big files: sharing via OneDrive, pasting in a transfer link, and compressing the file when that's enough.
Outlook's Attachment Limit Explained
The reason large files fail is a hard cap on attachment size, and it's smaller than most people expect. The classic Outlook desktop app and accounts running on Exchange default to roughly 20MB per message. Outlook.com on the web is similar — around 20MB per message — but instead of a flat rejection it usually prompts you to send anything larger as a OneDrive link instead.
It's worth knowing that 20MB is the default, not a guarantee. A company's mail server or IT admin can set the limit lower, so on a work account your effective cap might be 10MB or even less. And because email adds encoding overhead, a file that looks like it's just under the line on disk can still tip over once it's attached. The practical takeaway: if your file is more than a handful of megabytes, assume a plain attachment won't cut it and reach for one of the methods below.
None of this means Outlook can't send large files — it means the file itself shouldn't travel as a raw attachment. Instead, you send a link to the file, or you shrink the file until it fits. Every method that follows is just a version of one of those two ideas.
Method 1: Share via OneDrive
Outlook's own answer to the size limit is OneDrive, Microsoft's cloud storage. When you attach a file that's too big, Outlook offers to upload it to OneDrive and insert a share link in the email instead of the file itself. The recipient clicks the link and downloads (or previews) the file from the cloud. OneDrive can share files up to around 2GB this way — roughly a hundred times what a direct attachment allows.
To use it, attach your file as normal. If it's over the limit, Outlook prompts you to upload and share via OneDrive; on the desktop app you can also choose Attach File → Upload and share. Once it's uploaded, the email carries a link with view or edit permissions you can adjust.
The upside is that it's built right in and needs no extra tools. If you and your recipient both live inside Microsoft 365, this is often the smoothest choice — permissions, previews, and co-editing all work seamlessly. The trade-offs: you need a Microsoft account and the file counts against your OneDrive storage quota, so a big upload can eat into your space. Sharing settings can also be fiddly on work accounts where an admin restricts external links, and a recipient outside your organization may be asked to sign in or request access.
Method 2: Send a Transfer Link
If your file is bigger than OneDrive's ceiling, or you'd rather not deal with accounts and permissions at all, a dedicated transfer tool is the cleanest route. Realtime Sender is free, handles up to 30GB per file, and needs no account from you or the person receiving it. You upload the file once, then paste the resulting link or code into your Outlook email. Here's the whole process:
- Open the site. Go to realtimesender.com in any browser — nothing to install, and it works alongside Outlook in another tab.
- Drop in your file. Drag it onto the page or click to browse and select it. The upload starts right away and shows live progress.
- Copy the code or link. When the upload is ready, you get a short 6-character code and a share link.
- Paste it into your Outlook email. Write your message as usual and drop the code or link into the body. Send it — the email stays tiny because the file lives on the transfer server, not in the attachment.
- The recipient downloads it. They open the same site, enter the code (or click the link), and the file downloads straight to their device. No account needed on their end. Afterward it auto-deletes, so nothing lingers.
Because the 30GB free limit dwarfs the roughly 20MB attachment cap — and comfortably beats OneDrive's 2GB — there's no splitting, no upgrade prompt, and no sign-up wall. It's the method that scales when files get genuinely large.
Send your large file now
Realtime Sender is free with no account. Open it here, drop in your file, and paste the link into your Outlook email — your transfer starts in seconds.
Method 3: Compress the File
Sometimes the file is only a little over the line, and the simplest fix is to shrink it. Compressing into a .zip archive is built into both Windows and macOS: right-click the file (or folder), choose the compress option, and attach the resulting zip to your Outlook email. If it drops under the roughly 20MB limit, you're done — no links, no cloud, no extra tools.
When it helps: zipping works well for text-heavy files like documents, spreadsheets, presentations, and code, which can shrink dramatically. It's also handy for bundling several smaller files into one tidy attachment.
When it won't: files that are already compressed barely budge. Videos (MP4, MOV), photos (JPEG), music (MP3), and PDFs full of images are already packed tight, so a zip might shave off only a percent or two — nowhere near enough to squeeze a large media file under 20MB. If a quick zip test doesn't get you there, don't keep fighting it; switch to OneDrive or a transfer link instead.
Which Method Should You Use?
Each method suits a different situation, so here's an honest comparison to help you pick:
| Method | Max size | Needs account? | Notes |
|---|---|---|---|
| Direct attachment | ~20MB | No | Default Outlook limit; admins can set it lower |
| OneDrive link | ~2GB | Yes (Microsoft) | Built in; best if both sides use Microsoft 365 |
| Realtime Sender | 30GB | No | Free transfer link; recipient needs no account |
| Zip / compress | Depends | No | Only helps if it drops under ~20MB |
In short: if the file barely exceeds the limit and compresses well, zip it. If you're up to a couple of gigabytes and both you and the recipient live in the Microsoft ecosystem, OneDrive is a great built-in choice. And for anything very large — or when your recipient doesn't have (or doesn't want) a Microsoft account — a dedicated transfer link wins on both size and simplicity.
Tips
A few small habits keep large sends from going sideways, whichever method you choose:
- Check the file size first. Right-click and view properties before attaching. If it's over a few megabytes, plan for a link rather than fighting a bounce-back.
- Remember work limits can be stricter. On a company account the cap may be well under 20MB, so don't assume the default applies everywhere.
- Use a stable connection for big uploads. A 2GB OneDrive upload or a multi-gigabyte transfer runs longer, so wired or solid Wi-Fi beats mobile data.
- Confirm link permissions. With OneDrive, double-check whether the link is view-only or editable, and whether external recipients can open it without signing in.
- Zip many files into one. Even when you're sending a link, bundling a folder into a single .zip keeps everything together in one clean download.
If you keep running into the size error across different email providers, our guide on fixing "file too large to send" covers the wider picture beyond Outlook.
Frequently Asked Questions
What is the attachment size limit in Outlook?
The classic Outlook desktop app and Exchange accounts default to around 20MB per message, and Outlook.com on the web is also around 20MB. Your company's mail server or admin can set this limit lower, so the effective cap is sometimes smaller than 20MB.
How do I send a file that is too large for Outlook?
You have three practical options: upload the file to OneDrive and share a link (up to about 2GB), paste a transfer link from a tool like Realtime Sender into your email (up to 30GB free with no account), or compress the file into a zip if that gets it under the roughly 20MB limit.
How large a file can I send with OneDrive in Outlook?
When you attach a large file, Outlook offers to upload it to OneDrive and insert a share link instead. OneDrive can share files up to around 2GB this way, which is far more than the roughly 20MB attachment cap, though both you and ideally the recipient work best inside Microsoft 365.
Can I send large files in Outlook without a Microsoft account?
OneDrive sharing needs a Microsoft account. If you or your recipient would rather not use one, upload the file to Realtime Sender, which is free with no account for files up to 30GB, then paste the link or 6-character code into your Outlook email.
Does zipping a file let me email it in Outlook?
Zipping helps only when it pushes the file under the roughly 20MB attachment limit. It works well for documents and spreadsheets, but already-compressed files like videos, photos, and MP3s barely shrink, so a zip usually will not get them small enough to attach.