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Email attachment limits look simple until you actually hit one. You check that your file is under the number, hit send, and the message bounces anyway — or worse, it leaves your outbox and quietly fails to arrive. This page gives you the current limits for every major provider, then explains the two things that make those numbers misleading in practice.
The Limits, by Provider
These are the per-message limits each provider documents for standard consumer accounts:
| Provider | Documented limit | Realistic file budget | Built-in escape hatch |
|---|---|---|---|
| Gmail (personal) | 25 MB | ~18 MB | Google Drive link |
| Outlook.com | 25 MB | ~18 MB | OneDrive link |
| Yahoo Mail | 25 MB | ~18 MB | None built in |
| iCloud Mail | 20 MB | ~14 MB | Mail Drop (up to 5 GB) |
| Proton Mail | 25 MB | ~18 MB | Proton Drive link |
| AOL Mail | 25 MB | ~18 MB | None built in |
One honest caveat on Outlook: Microsoft's own documentation isn't entirely consistent here. The Outlook.com web limit is documented as 25MB, while Microsoft's help pages for the Outlook desktop app separately cite a 20MB figure, and corporate Exchange administrators can set their own ceiling entirely. If you're on a work account, 20MB is the safer assumption.
Why 24MB Fails a 25MB Limit
This is the part almost nobody explains, and it's the single most common reason a "within the limit" attachment bounces.
Email was designed to carry text. To send a binary file — a photo, a PDF, a video — the file has to be converted into text first, using an encoding called base64. That conversion is not free: base64 inflates the data by roughly 33%, and line-wrapping pushes the real-world overhead closer to 37%.
So when you attach a 24MB file to a message with a 25MB limit, the message that actually travels is around 32MB. It exceeds the cap and gets rejected, even though the file on your disk was comfortably under the number.
The practical rule to carry away:
- 25MB limit → keep files under about 18MB.
- 20MB limit → keep files under about 14MB.
Those are the numbers in the third column of the table above. They're the ones worth actually remembering.
Your Real Limit Is the Smaller of Two
The second trap: there are always two limits in play, and the stricter one decides.
Your provider has to accept the message for sending, and your recipient's provider has to accept it for delivery. Those caps are often different, and you have no visibility into theirs.
A concrete example. You're on Gmail with a 25MB limit and you send an 18MB attachment to a colleague on iCloud Mail, which caps at 20MB. Gmail accepts it. Once encoded it's roughly 24MB, which blows past iCloud's 20MB ceiling, so it bounces on arrival — or lands in a bounce report you might not read carefully.
This is why "it worked when I sent it to myself" is such a common and misleading test. Sending within one provider only tests one of the two caps.
It's Per Message, Not Per File
One more frequent misunderstanding: the limit applies to the entire message, not to each attachment individually. That total includes:
- Every attachment added together, after encoding
- The message body and subject
- Headers and routing information
- Your signature — including any logo image in it
- Inline images pasted into the body
So attaching three 9MB photos to a Gmail message doesn't give you 27MB against a 25MB limit — it gives you roughly 36MB encoded, and it won't send. And if your signature carries a 200KB logo, that counts too.
What to Do Instead
Once you're over the limit, there are really only three honest options.
1. Make the file smaller. Sensible when you're slightly over. Compress a PDF, resize photos down from full camera resolution, or re-encode a video at a lower bitrate. Pointless when you're wildly over — you can't shrink a 2GB video to 18MB and still have something worth watching.
2. Use your provider's cloud hook. Gmail will offer to replace an oversized attachment with a Drive link; Outlook does the same with OneDrive; Apple Mail has Mail Drop, which handles up to 5GB. These work well and cost nothing extra if you already use that ecosystem. The trade-offs are that it consumes your storage quota, the file sits there until you remember to clean it up, and you have sharing permissions to think about.
3. Send a transfer link. Upload the file to a transfer tool and paste the link or code into your email. The email itself stays tiny, so no attachment limit on either end applies. This is the cleanest option for a one-off send, for a recipient outside your organisation, or when you'd rather the file didn't live in your cloud storage indefinitely.
Over the limit?
Open Realtime Sender, drop in your file (up to 30GB, free, no account), and paste the code into your email. The file is deleted automatically after download, so there's nothing to clean up later.
Business Accounts Are Different
If you're on a work account, the consumer numbers above may not apply to you at all.
Google Workspace sends up to 25MB on most plans, with higher-tier plans permitting up to 50MB from the Gmail web interface, and receive limits that run higher still. Microsoft 365 and Exchange default to around 25MB but administrators can configure that upward substantially — or downward, which catches people out.
The practical implication: on a corporate account, don't trust a blog post, including this one. Send yourself a test message at the size you care about, or ask IT. And remember the two-cap rule — your generous 50MB send limit does nothing for a recipient whose provider stops at 20MB.
Frequently Asked Questions
What is the maximum email attachment size?
Most consumer email providers cap a single message between 20MB and 25MB. Gmail, Yahoo, Proton Mail and AOL document 25MB, while iCloud Mail documents 20MB. Because of encoding overhead, the largest file you can actually attach to a 25MB limit is closer to 18MB.
Why did my 24MB attachment fail on a 25MB limit?
Attachments are encoded into the message using base64, which inflates binary data by roughly a third. A 24MB file becomes about 32MB on the wire, which exceeds a 25MB message limit. Plan for about 18MB of real file against a 25MB cap.
Is the limit per file or for the whole email?
For the whole message. The cap covers every attachment added together, plus the message body, headers, your signature and any inline images. Three 9MB files will not fit under a 25MB limit once encoding is applied.
Whose limit applies, mine or the recipient's?
Both, and the smaller one wins. Your provider has to accept the message for sending and theirs has to accept it for delivery. If you send 24MB from a 25MB account to someone on a 20MB account, it can leave your outbox and still bounce.
How do I email a file that is over the limit?
Do not attach it. Upload the file somewhere and email a link instead. Gmail offers Drive integration, Outlook offers OneDrive, and Apple Mail has Mail Drop for up to 5GB. For a one-off transfer with no account or storage quota involved, a temporary transfer tool gives you a link or code to paste into the email.