The 33% Base64 MIME Encoding Inflation Factor
Email protocols (SMTP) cannot send raw binary files; attachments must be encoded as ASCII text using Base64. Base64 encoding represents every 3 bytes of binary data as 4 ASCII characters, introducing an unavoidable 33% file size inflation.
This means a 20MB PDF file balloons to approximately 26.6MB when attached to an email, triggering immediate server rejections even though the file on your hard drive was technically under 25MB! Target an uncompressed size below 18MB to be safe.
Downsampling Resolution from 600 DPI to 150 DPI
Scanned office PDFs are often captured at print-press resolutions (300 to 600 DPI). Computer and smartphone screens only display between 72 and 150 DPI.
Downsampling embedded raster graphics to 150 DPI with WebP or high-quality JPEG compression sheds up to 85% of total file size with zero perceptible loss in screen readability.
Step-by-Step Tutorial
Check Uncompressed File Size
Ensure target file size is under 18MB to allow for the 33% Base64 MIME email inflation.
Apply In-Browser Compression
Drag your file into DocSwift Compress PDF and select the Email-Optimized preset.
Send Without Bouncebacks
Attach your slimmed PDF directly to your email draft with 100% confidence of delivery.
Ready to Try It Yourself?
DocSwift processes everything directly on your device. Fast, safe, and completely free forever.
How helpful was this guide?
Rated 4.9 / 5 by 3,420+ users worldwide
Share with Colleagues & Friends
Help others protect their document privacy
Frequently Asked Questions
Why did my 23MB PDF get rejected by Gmail if the limit is 25MB?
Base64 email MIME encoding expands file sizes by 33%. A 23MB PDF becomes ~30.6MB in transit, causing mail servers to bounce the message.
Are my private financial attachments uploaded to DocSwift servers?
No. All PDF compression occurs entirely in client-side WebAssembly within your local browser memory. No files are ever uploaded.