You try to send a PDF by email and get bounced: "attachment too large", "message size exceeded", "file too big to send." Annoying. The limits are tighter than most people realise — and there is a Base64 wrinkle at the end of this article that explains why a 22 MB file can still fail Gmail's 25 MB limit. Here is the full picture and how to fix it fast.
Email attachment size limits (quick reference)
- Gmail: 25 MB per message (including all attachments)
- Outlook.com / Hotmail: 20 MB per message
- Microsoft 365 (business): Typically 25–35 MB, set by admin
- Yahoo Mail: 25 MB per message
- Apple iCloud Mail: 20 MB (uses Mail Drop for larger files)
- Corporate mail servers: Often 10–20 MB — sometimes even 5 MB
In practice, keep email attachments under 10 MB to be safe across all recipients. Under 5 MB is ideal.
Why PDFs get so large
- High-resolution embedded photos. A PDF with ten 12-megapixel photos can easily be 40–60 MB. Each photo is stored at full camera resolution unless the PDF creator compressed them.
- Presentation exports (PowerPoint/Keynote to PDF). Every slide's background, graphics, and photos are embedded at high resolution. A 30-slide deck often exports to 20–80 MB.
- Scanned documents. Each page is a high-resolution photo. A 20-page scan at 300 DPI is 15–25 MB.
- Embedded fonts. Some PDFs embed full font files (not subsets) — adding 2–10 MB for each typeface used.
- Redundant metadata. Some PDF creation tools embed thumbnails, revision history, and comments that add to file size without adding visible content.
Fix 1: Compress the PDF (fastest)
Filero's free Compress PDF tool typically reduces photo-heavy PDFs by 60–80% in about 10 seconds. A 40 MB presentation PDF usually compresses to 4–8 MB — well within email limits.
- Open the Compress PDF tool.
- Upload your PDF.
- Choose Balanced (150 DPI) for most uses, or Small File (72 DPI) for screen-only documents.
- Download the compressed PDF and attach to your email.
Fix 2: Remove unnecessary pages first
If the PDF contains pages the recipient does not need — blank pages, cover sheets, appendices, unused slides — remove them before compressing. Use Filero's Split PDF tool to extract only the pages required. Fewer pages means a smaller file before compression even runs.
Fix 3: Share via Google Drive or cloud link instead
Honestly, for anything over 10 MB, a link is the better approach regardless of whether the file compresses well. Attachments clog inboxes, hit limits, and make emails feel heavy. A link is cleaner for everyone.
- Google Drive: Upload the PDF, right-click → Share → Anyone with the link → Copy link. Paste the link in your email. The recipient downloads it at full quality.
- Dropbox or OneDrive: Same principle — upload and share the link.
- WeTransfer: Free for files up to 2 GB — ideal for large one-off transfers. No account needed.
Fix 4: Export at lower quality from the source
If you are creating the PDF yourself, configure the export correctly before it becomes a large file:
- Word: File → Save As → PDF → Optimise for: Minimum size (publishing online)
- PowerPoint: File → Export → Create PDF/XPS → Options → "Minimum size" or reduce image resolution in the settings
- Mac Print dialog: When printing to PDF, choose the "Reduce File Size" PDF filter in the Quartz Filter option
Frequently asked questions
My PDF is only 5 pages but still 30 MB — why?
Almost certainly high-resolution embedded images. Five pages with professional photography, full-bleed graphics, or exported presentation slides can be 30+ MB. Use the Compress PDF tool — the Balanced preset will typically reduce this to 3–6 MB.
Gmail says my file is too big even though it is under 25 MB — why?
This trips people up constantly. Email attachments are encoded in Base64 when transmitted, which inflates the file size by roughly 37%. So a 20 MB PDF becomes about 27 MB inside the email — over Gmail's 25 MB limit. The practical rule: keep attachments under 18 MB to be reliably safe within Gmail. Anything bigger, send a Drive link.
Why does my PowerPoint PDF export end up so much larger than the original .pptx?
A .pptx file stores images in a compressed format internally. When PowerPoint exports to PDF, it decompresses those images and re-embeds them at full resolution — often resulting in a PDF that is 3–5× the size of the original PowerPoint file. The fix is to use PowerPoint's "Minimum size" export option, or run the resulting PDF through Filero's Compress PDF tool before sending.
Ready to try it?
Use Filero's free Compress PDF tool. No account needed, works on any device.
Open Compress PDF