March 22, 2026
You have probably been there. The report is done, the contract is signed, you hit "Send" on your email, and it bounces back with a message about attachment size limits. A single PDF, and somehow it is too big to send.
The problem is that email providers have strict attachment limits, and PDFs -- especially ones with images or scanned pages -- blow past those limits more often than you would think.
How Large Can Email Attachments Be?
Here is a quick rundown of the major providers:
- Gmail: 25MB
- Outlook / Hotmail: 20MB
- Yahoo Mail: 25MB
- Corporate Exchange servers: usually 10MB, sometimes as low as 5MB
- Government email systems: typically 10-15MB
Keep in mind that these are sender-side limits. If the person you are emailing has a smaller limit on their end, your message will still bounce. In practice, keeping attachments under 10MB is the safest bet.
Why Is Your PDF So Large?
A plain-text PDF is usually just a few hundred KB. You will rarely have trouble sending one. But certain things cause PDFs to balloon in size:
- Scanned documents: each page is a full-resolution image. At 300 DPI in color, a single page runs about 8MB
- Embedded high-res photos: reports and presentations with original camera photos can get huge
- Large page counts: even modestly-sized pages add up over 50+ pages
- Embedded fonts: some PDFs embed entire font families, adding several MB
A 20-page scanned contract can easily hit 40MB or more. That is well over every email provider's limit.
Three Steps to Compress Your PDF
Using PDF Under's compress tool, the whole process takes about a minute:
- Open the compress tool and drag your PDF into the upload area (or click to select a file)
- Set your target file size. If you are not sure what to pick, 8MB is a safe choice that works with virtually every email provider
- Click "Start Compressing." The tool automatically finds the best quality at your target size. Download the compressed version when it is done
Everything happens in your browser. Your PDF is never uploaded to any server. If your file contains sensitive contracts or financial data, you can use it without worry.
Will Compression Make My PDF Blurry?
This is the most common concern, and the honest answer is: it depends on how much you compress.
Going from 40MB down to 8MB (a 5x reduction) is usually fine for scanned documents. Text stays readable, and you would only notice quality loss if you zoom past 200%. For email purposes, where the recipient just needs to read the document, this level of compression is more than adequate.
Going down to 2MB from a large starting point means more visible quality loss. Still readable, but noticeably softer. For most email attachments, that trade-off is worth it.
Practical Tips
- Compress before sending: do not wait for the bounce-back notification. Get in the habit of checking file sizes before attaching
- Multiple attachments: if you are sending several PDFs, compress each one to under 5MB to stay safely within limits
- Very large files: if your PDF is over 25MB, consider sharing it via Google Drive or Dropbox instead of compressing it down. Quality loss from extreme compression may not be worth it
- Remember the recipient: even if your email provider allows 25MB attachments, the recipient's server might only accept 10MB
Next time you get that dreaded "attachment too large" message, you know what to do. Three steps, one minute, problem solved.