You hit Send and get a bounce: "Message size exceeds the limit." Or worse, the email leaves your outbox but never reaches the other person because their company server silently rejects anything over 10 MB. Compressing the PDF before attaching it solves both problems.
Know the Limits
- Gmail: 25 MB per message (larger files are offered as a Google Drive link).
- Outlook.com: usually 20 MB.
- Company and government mail servers: often 10 MB, sometimes as low as 5 MB.
- Attachments grow by roughly a third when sent, because email encodes files as text.
So a 20 MB PDF can fail even on a 25 MB service. A good target is under 5 MB, and under 2 MB when you are unsure.
How to Compress a PDF for Email
- Open Compress PDF.
- Upload the file.
- Choose ebook — it keeps text crisp and photos clear on screen.
- Download the compressed version and check it before attaching.
- Rename it clearly, for example *Invoice_March_Ahmed_Traders.pdf*, so it looks professional.
If You Need It Even Smaller
- Try the screen level. It lowers image resolution further and is fine for reading.
- Remove pages the recipient does not need using Remove Pages.
- Split a long report into chapters with Split PDF and send them in separate emails.
- If the file is a scan, rescan in greyscale at 150–200 DPI — see why some PDFs are so large.
Sending Several PDFs?
Rather than attaching six files that together exceed the limit, merge them into one document and compress the result. One tidy attachment is easier for the recipient to open and file.
Before You Hit Send
- Open the compressed PDF and zoom to 150% — are signatures, stamps and small print readable?
- Check the page order.
- Confirm the final size in your file manager.
- Mention in the email body what the attachment contains.
When Not to Attach
If a document is over 25 MB even after compression — a large scanned archive or a design portfolio — upload it to a cloud drive and share a link. Set the link to "view only," and tell the recipient how long it will stay available.
For more ways to reduce size, read our guide on reducing PDF file size online.
Compressing on a Phone
If you are replying from your phone, you do not need a computer. Open Compress PDF in your mobile browser, tap the upload area, and pick the file from Downloads, WhatsApp documents or your Files app. After compression, the download goes back to the same Downloads folder, and you can attach it from Gmail or Outlook as usual.
Which Level for Which Email
| Email type | Suggested level | Why |
|---|---|---|
| Invoice or quotation to a client | Ebook | Logos and tables stay crisp |
| Scanned documents to an office | Ebook, then screen if needed | Offices often have 10 MB limits |
| Design proof or print-ready file | Printer, or send a link | Quality matters more than size |
| Quick reference for a colleague | Screen | Only needs to be readable |
Common Mistakes
- Compressing a file that is already small. A 300 KB invoice does not need compression; it will barely change.
- Forgetting the total. Three 9 MB attachments are 27 MB together, even if each one looks fine.
- Renaming carelessly. Names like *scan0001_final_final.pdf* look unprofessional and are hard to find later.
