Know your real limit (it is lower than the number)
Gmail and Yahoo cap attachments at 25MB; Outlook.com is around 20MB. But email encodes attachments in a format called Base64 that adds roughly 33% to the size in transit, so a 24MB file can arrive as about 32MB and bounce. Aim for around 75% of the published limit, under about 18MB for Gmail and under about 15MB for Outlook, to stay safe across providers.
Compress first, it usually fixes it
PDF compression mainly optimizes embedded images and strips redundant data, while text and vector content stay sharp. Image-heavy PDFs such as scans, brochures, and slide decks often shrink 50-90%, which is normally more than enough to clear an email limit. Text-only PDFs are already small, so expect only modest gains there.
Do it without uploading the file
Most compress-PDF-for-email tools upload your document to a server first. For a contract, invoice, ID, or client file, that is avoidable exposure for a purely mechanical task. Just Compress runs supported PDF compression locally in your browser and in the iOS app: pick the file, choose a quality preset, and download the smaller copy. The file never leaves your device just to be resized.
If compression is not enough
For very large or scan-heavy PDFs, split the PDF and send only the pages the recipient needs, or send a link instead, since Gmail automatically offers a Google Drive link for files over 25MB. Zipping a PDF rarely helps much because PDFs are already compressed internally.
FAQ
What size should a PDF be to email it?
Aim for under about 18MB for Gmail and Yahoo, and under about 15MB for Outlook. The published limits are 25MB and around 20MB, but transfer encoding inflates the size by roughly a third, so staying near 75% of the limit avoids bounces.
Will compressing a PDF make it blurry?
Text and vector graphics stay sharp. Compression mainly reduces image resolution and quality, and at normal viewing sizes the difference is usually hard to notice. Use a balanced preset for documents that need to stay clearly readable.
Can I compress a PDF for email without uploading it?
Yes. Just Compress compresses supported PDFs locally in your browser or iOS app, so a private document is not sent to a server just to be made smaller.
Why did my email bounce even though the PDF was under 25MB?
Email encodes attachments in Base64, which adds about 33% to the size in transit. A 24MB file can become about 32MB on send and exceed the limit. Compress to roughly 75% of the cap to be safe.
How do I email a PDF that is too big on my iPhone?
Compress it first with the Just Compress iOS app, then attach the smaller copy. If it is still too large, send an iCloud or Drive link instead.