How to reduce a PDF file size for email
Compress the PDF to a 150 DPI target first, which is enough for on-screen reading and usually gets a scan under 5 MB. Gmail and Yahoo cap attachments at 25 MB, Outlook.com and iCloud Mail at 20 MB, and MIME encoding adds about 33 percent, so aim below 18 MB.
The bounce message says "message too large" and gives you no number to work with. Here are the real numbers, and what to do when your file is over them.
Attachment limits by service
| Service | Stated limit | Safe real file size | Larger files |
|---|---|---|---|
| Gmail | 25 MB per message | ~18 MB | Auto-offers a Google Drive link |
| Outlook.com | 20 MB per message | ~14 MB | OneDrive link |
| Microsoft 365 / Exchange Online | 25 MB default, admin-configurable to 150 MB | ~18 MB unless raised | OneDrive or SharePoint link |
| iCloud Mail | 20 MB per message | ~14 MB | Mail Drop, up to 5 GB, link expires in 30 days |
| Yahoo Mail | 25 MB per message | ~18 MB | Cloud link |
| Proton Mail | 25 MB per message | ~18 MB | Proton Drive link |
| Typical corporate gateway | 10 MB | ~7 MB | Ask IT, or use a file share |
| WeTransfer (free) | 2 GB per transfer | 2 GB | Not email, a download link |
Email attachments are encoded in base64 before they travel, which turns every 3 bytes into 4. That is roughly 33 percent overhead. A 24 MB PDF becomes about 32 MB on the wire and will be rejected by a 25 MB limit. This is why your "under the limit" file bounced.
The recipient limit matters too, and you cannot see it. Sending 20 MB from Gmail to someone whose employer caps inbound mail at 10 MB fails silently or bounces hours later. For anything above 10 MB, a link is more reliable than an attachment.
Get the file under the limit
- Check the actual sizeRight-click the file → Properties on Windows, or Get Info on macOS. Use the size in MB, not the "size on disk".
- Run a lossless passOpen the PDF compressor and compress without downsampling. If that alone clears the limit, you are done and nothing was degraded.
- Downsample to 150 DPIIf it is still too big, target 150 DPI. That is sharp on any screen and on most office printers, and it is the single biggest win for scanned documents.
- Drop colour if the source is textA black-and-white scan stored as 24-bit colour is carrying three channels of nothing. Converting to greyscale typically removes another 60 percent.
- Re-check and sendConfirm the new size, open the file once to make sure it still reads properly, then attach it.
Compress the PDF in your browser first, the file never leaves your computer.
Compress PDF →Split it instead
A 60 MB report will not compress to 18 MB without becoming unreadable. Splitting is the honest alternative: send chapters 1-3 in one mail and 4-6 in another, or send only the pages the recipient asked for. Use extract pages when you need a specific range, or the splitter to cut at chapter boundaries. There is a full walkthrough in splitting a large PDF for email.
Send a link instead of a file
- Google Drive, in Gmail, click the Drive icon in the compose toolbar. Gmail offers this automatically once your attachment exceeds 25 MB. Set sharing to "Anyone with the link" or the recipient gets a permission-request loop.
- OneDrive, in Outlook, Insert → Link → Browse this computer, then choose "Upload and share". Recipients outside your tenant may need the link set to "Anyone".
- iCloud Mail Drop, Apple Mail offers this at 20 MB. Files stay available for 30 days and do not count against your iCloud storage.
- WeTransfer, no account needed on the free tier, 2 GB per transfer, and the recipient gets a plain download page. Good for one-off sends to people outside your organisation.
A shared link also fixes the version problem. If you find a mistake after sending, you replace the file at the link. An attachment sits in the recipient inbox forever in its wrong version.
Before you send anything
A PDF carries the author name, the software that made it, and often the full path of the folder it was saved in. If the file is going outside your organisation, strip the metadata first. It takes a few seconds and costs nothing in file size.
If the file only got large because it is a scan, the deeper fix is on the scanner: 200 DPI greyscale for text documents, 300 DPI colour only when the colour matters. See why your PDF is so large for the rest of the causes.
Frequently asked questions
What is the maximum PDF size I can email?
Gmail and Yahoo allow 25 MB per message, Outlook.com and iCloud Mail 20 MB, and many corporate gateways cap at 10 MB. Because base64 encoding adds about 33 percent, keep the actual file under 18 MB for a 25 MB limit and under 14 MB for a 20 MB limit.
Why does my 20 MB PDF fail to send on a 25 MB limit?
Attachments are base64-encoded for transport, which inflates them by roughly a third. A 20 MB file becomes about 27 MB on the wire. Add the message body and headers and it crosses a 25 MB limit.
How do I email a PDF that is 100 MB?
Do not attach it. Upload it to Google Drive, OneDrive, Dropbox or WeTransfer and send the link. If the recipient insists on an attachment, split the PDF into parts under 18 MB each and send several messages.
Does zipping a PDF make it smaller?
Barely. PDF content streams are already Flate-compressed, so a ZIP typically saves 2-5 percent. Zipping is useful for bundling several files into one attachment, not for reducing size.
What DPI should I use for a PDF I am emailing?
150 DPI. It is crisp on any screen, prints acceptably on an office laser printer, and cuts a 600 DPI scan by roughly 94 percent. Use 300 DPI only when the recipient will print the document properly.