How to Get a PDF Under an Email Attachment Limit
Updated August 29, 2026
Your email bounced, the file is 24 MB, and the limit says 25 MB. That isn't a mistake — attachments get bigger in transit, and almost nobody tells you by how much. Here's the real number to aim for, and what each provider actually allows.
The short answer
Against a 25 MB limit, aim to get the PDF under about 18 MB. If you don't know what the recipient's mail system allows, under 7 MB is genuinely safe for everyone. Compress the file with the PDF Compressor; if that isn't enough, send fewer pages with Split PDF; if it still won't fit, send a link instead.
The headroom isn't superstition. It's the next section, and it's the part that surprises people.
Why a 24 MB file fails a 25 MB limit
Email can't carry raw binary files, so every attachment is re-encoded into plain text before it's sent. That encoding makes the file meaningfully bigger in transit than it is on your disk — and the limit is applied to the encoded size, not the size you see in your file manager.
Both major providers document the overhead. Microsoft states that messages routed outside its datacenters are “subject to an additional 33% translation encoding increase.” Google says its Workspace size limits “are the limit after encoding, which adds about a 37% increase.”
So a 20 MB PDF arrives at the limit check as roughly 26–27 MB, and a 25 MB cap rejects it. Working backwards from a 25 MB limit gives you about 18 MB of actual file — which is where the number in the short answer comes from.
Microsoft's own webmail quietly does this maths for you: it “restricts the size of message you can send to 25% less than the configured setting.” Most other clients don't, which is why the failure feels arbitrary. Notably, Google's help page for personal Gmail doesn't say whether its 25 MB applies before or after encoding — another reason to leave room rather than test the edge.
What each provider actually allows
There is no single “email limit,” and there isn't even a single Outlook limit — Microsoft publishes several different numbers depending on which Outlook you mean. All figures below are the providers' own published limits, and they apply to the whole message, not one attachment.
| Mail service | Attachment limit | Worth knowing |
|---|---|---|
| Gmail (personal) | 25 MB | Above it, Gmail swaps the attachment for a Drive link automatically |
| Outlook.com | 25 MB | Up to 2 GB if you share via OneDrive instead |
| Outlook desktop (personal account) | 20 MB | Microsoft's stated limit for internet email accounts |
| Outlook desktop (work/Exchange) | 10 MB by default | Your IT admin may have raised it — or not |
| Microsoft 365 / Exchange Online | 35 MB send by default | Admins can set anywhere from 1 MB to 150 MB |
| Outlook on iPhone or Android | 33 MB | Applies even when the organisation allows more |
| Yahoo Mail | 25 MB | Same limit for incoming and outgoing mail |
| iCloud Mail | 20 MB | Up to 5 GB with Mail Drop turned on |
The limit that matters is your recipient's
This is the part that catches people out. Your outgoing limit only gets the message sent — the receiving system then applies its own. Microsoft says so plainly: some email clients “may have lower message size limits or may limit the size of an individual file attachment to a value that is less than the Exchange Online message size limit.”
A 30 MB attachment can leave a generous work account and still bounce off a recipient's 10 MB one. When you don't know what's on the other end, under 7 MB clears every limit in the table above even after encoding — including a default 10 MB Exchange account.
Getting the file down, in order
- Compress it. Run the PDF through the PDF Compressor on Balanced, then Strong if you need more. The before-and-after readout tells you exactly where you landed.
- Send fewer pages. Often the recipient needs three pages of a forty-page document. Extract just those pages — pages you don't send weigh nothing, and this beats any compression setting.
- Fix the source, if it's a scan. Re-scanning at 150 DPI in grayscale instead of 600 DPI in colour starts you several times smaller.
- Send a link instead. For genuinely large documents this is the honest answer, and Gmail already does it for you above 25 MB.
When compressing barely helps
Open the PDF and try to select the text with your cursor. If you can, it's a born-digital document — exported from Word, or an invoice or form — and its text is already stored efficiently. There's little for a compressor to squeeze, and it may hand your file back unchanged rather than make it bigger. That isn't a failure; it means the size is coming from somewhere else, usually the page count or an embedded image.
If the text can't be selected, it's a scan — a photograph of paper. Those compress dramatically, and this is where the compressor earns its place.
Chasing a specific number rather than an email limit? Compressing to 100 KB, 200 KB, or 1 MB covers what's realistic at each target.
What compressing costs you
Browser-side PDF compression rebuilds each page as an optimised image. That's why scans shrink so much — but in the compressed copy the text stops being selectable and searchable, and any form fields are flattened into the page. Keep your original for editing and send the compressed copy. If the recipient needs to search or fill in the document, send fewer pages instead of compressing harder.
One thing worth knowing if the document is confidential: our compressor runs entirely inside your browser, so the file is never uploaded anywhere on its way to getting smaller. Tools that promise to delete your files after an hour are telling you a copy reached their server first.
Common questions
- Why was my email rejected when the file was under the limit?
- Attachments are re-encoded for transit, which inflates them by roughly a third, and the limit is checked against that larger encoded size. Aim for about 18 MB against a 25 MB limit.
- What is the Outlook attachment limit?
- There isn't one number. Outlook.com allows 25 MB, Outlook desktop with a personal account 20 MB, a work Exchange account 10 MB by default, Microsoft 365 35 MB by default, and Outlook on iPhone or Android 33 MB.
- Does the recipient's limit matter more than mine?
- Both apply, and the smaller one wins. Your message has to pass your sending limit and their receiving limit, so a file that sends fine can still bounce on arrival.
- Why did compressing barely shrink my PDF?
- Because it is probably a born-digital document whose text is already stored efficiently. If you can select the text with your cursor, there is little left to compress — reduce the page count instead.
- Will the recipient still be able to search the text?
- Not in a compressed copy. Compression rebuilds each page as an image, so text stops being selectable and searchable and form fields are flattened. Send fewer pages if searchable text matters.
- Is it safer to send a link instead?
- For very large files it is usually the practical choice, and Gmail does it automatically above 25 MB. For confidential documents, note that a link means storing the file on a cloud service, while compressing it in your browser does not.