What is the maximum email attachment size?

For most people, 25 MB. That is the cap on Gmail, Yahoo and Outlook.com, and it applies to the whole message rather than to each file. Some providers differ — iCloud Mail is 20 MB, Fastmail is 70 MB, and a Microsoft 365 administrator can raise their organisation's limit as high as about 150 MB. The safe number to design around is 10 MB, because that clears everything.

Why did my email bounce when the file was under the limit?

Two limits always apply: yours and the recipient's. The smaller one decides. A 30 MB attachment can leave a Microsoft 365 outbox happily and bounce off a company mail server still running a 10 MB default from years ago. There is also encoding overhead, which inflates every attachment by roughly a third before it is measured.

Does the attachment limit apply per file or per email?

Per email, including everything in it. Four 7 MB photos are a 28 MB message, not four files comfortably under 25 MB. Headers, the message body and any signature image count too, which is why a message that looks like it should just fit often does not.

How do I send a file bigger than the email limit?

Do not attach it — send a link. Gmail and Outlook both offer this natively by pushing the file to Drive or OneDrive and inserting a link, and that is fine for internal use. For client work a proper transfer link is better, because you can set an expiry, add a password, and see when it was collected.

Why is the email attachment limit still 25 MB?

Because email was never designed to move files, and the limit protects mail servers rather than users. Attachments are encoded into the message itself, so every server along the way has to hold the whole thing. Storage got cheap, but the protocol did not change, and a number set when broadband was new is still the number today.

Email Attachment Size Limits, Every Provider (2026)

Gmail is 25 MB. Outlook depends on who set it up. Every provider's limit, why your 22 MB file still bounced, and what to send instead.

The short version, as of September 2026:

Provider	Limit	Worth knowing
Gmail	25 MB to send, 50 MB to receive	Workspace Enterprise Plus rose to 50 MB in February 2026
Outlook.com	~25 MB	Some paths through the web app allow a little more
Microsoft 365	35 MB by default	An administrator can raise it to around 150 MB
Exchange (on-premise)	Often 10 MB	Whatever IT set, frequently years ago
Yahoo Mail	25 MB
iCloud Mail	20 MB	Mail Drop handles up to 5 GB by link instead
Proton Mail	25 MB	Higher totals on paid plans, split across attachments
Fastmail	70 MB	Generous, and largely irrelevant — see below

Now the parts that actually explain your bounced email, because the table is not really why you are here.

Both limits apply, and the smaller one wins

This is the single most useful thing on this page.

Your limit governs whether the message leaves. The recipient’s limit governs whether it arrives. They are set by different organisations who have never spoken to each other, and the smaller of the two decides.

So a 60 MB attachment leaves a Fastmail account without complaint and dies on arrival at a client running Exchange with a 10 MB cap. Your sent folder says it went. Either nothing tells you it didn’t land, or a bounce notice arrives hours later that nobody reads to the end.

This is why “my provider allows 70 MB” is not a plan. You are not sending to your provider.

Your 25 MB file is not 25 MB

Attachments do not travel as files. They are encoded into the text of the message using base64, which turns three bytes into four — an inflation of roughly 37% before anything else is counted.

So against a 25 MB ceiling you have about 18 MB of actual file. Then subtract the message body, the headers, and the 40 KB signature image with the logo and four social icons in it.

This is why a 22 MB video “under the limit” bounces, and why the error never explains itself. You were measuring the file. The mail server was measuring the message.

Corporate mail is stricter than any of this

If you send to businesses, the published limits above are the optimistic case. Beyond size, a corporate mail gateway may:

Strip attachments by type. Zip files are the usual casualty, because they are also how malware travels. Your carefully packaged delivery arrives as an email with nothing in it.
Quarantine the message for review, so it turns up three days later, or never, and nobody tells the sender.
Run an old, low limit, because raising it was never anybody’s job.

You will not be told any of this happened. The most common outcome of a too-large attachment is not an error message. It is silence, followed by “did you get that?”, followed by resending it, followed by more silence.

The number to actually design around

Ten megabytes. Under 10 MB an attachment clears essentially every provider, survives the encoding overhead, and gets through most corporate gateways.

Above 10 MB you are gambling. Above 25 MB you are not sending an email, you are generating a bounce.

What to send instead

Compress it first, if it is compressible. Most oversized PDFs are large because of images at print resolution in a document nobody will print. Exporting properly often takes a 40 MB file under 10 MB with no visible difference. A folder of documents zips well. Video and photography are already compressed and will not shrink meaningfully.

Use the built-in link. Attach something oversized in Gmail and it offers to upload to Drive and insert a link; Outlook does the same with OneDrive. This works, it is free, and for internal files it is the right answer. The catch is that you are handing over a doorway into your own storage, with sharing permissions you have to get right every time and no natural expiry.

Use a transfer service for one-off large files going outside the company. The options are compared here.

Send a link to a document, not a document. For anything that gets read rather than edited — a proposal, a report, a brochure, a deck — the attachment was never the right format. A link opens on a phone, cannot be too big for anyone’s inbox, updates without a resend, and tells you when it was read. The longer argument is here.

If you are doing this for a living

There is a difference between “this file is too big for email” and “we send large files to clients every week”. The first is a nuisance. The second is a workflow, and it deserves better than whatever is free and to hand.

The questions then are not about size at all. Can you choose how long the link lives? Can you kill it when you send the wrong version? Do you find out when it was collected, and by whom? And whose brand is on the download page — because that last one is free to claim and most people give it away.

We built Transfers around exactly that, and it is coming soon on the Living Page Agency plans.

Provider-specific detail

I’m Richard, and I build Living Page — a way to send documents and large files as links that open anywhere, carry your brand, and tell you when they land. Try it free.