Email size limits
Gmail: 25 MB per message before encoding (~18 MB in practice). Outlook: 20 MB default. Many corporate mail servers cap at 10 MB end-to-end.
The practical caps are tighter than the documented ones because email attachments are base64-encoded for transit, which inflates them by about 35%. A 20 MB file becomes a 27 MB attachment on the wire, which exceeds Gmail's 25 MB documented limit. Always plan for that overhead — aim for 70-75% of the documented cap as your real ceiling.
Corporate mail filters often impose tighter limits than the platform documentation suggests. A 10 MB attachment that Gmail accepts may be silently bounced by the recipient's Exchange server because the corporate policy capped inbound mail at 5 MB. The sender usually gets a delivery failure notice, sometimes hours later. To be safe across all destinations, target attachments under 5 MB.
Quick fix
Compress each photo at JPG quality 70 before attaching.
- Open the Image Compressor.
- Drop the photo (5 MB max per file).
- Move quality to 70.
- Click Compress, then Download.
- Attach to your email.
Sending several at once
Compress each one individually, then attach them all to the email. Zipping JPGs together adds almost no extra savings (JPG is already compressed), so don't bother unless your recipient prefers a single archive.
If you have more than about ten photos to send, the right answer is a shared link rather than direct attachments. Google Drive, Dropbox, and OneDrive all generate sharable links in a few clicks. The recipient gets the originals (no quality loss), the email stays small, and bounces from corporate size limits go away.
For bulk transfers of professional photos, services like WeTransfer accept up to 2 GB on the free tier and don't require an account on either end. The recipient gets a download link that expires in seven days — convenient for sharing wedding or event photos that the recipient will save once and not refer to again.
Real-world: how much shrinking is needed
A typical iPhone 15 photo runs 3-5 MB at full resolution. Three photos like that already approaches the 10 MB corporate cap. After quality-70 compression, the same photos drop to 400-600 KB each, letting you send 10-15 of them in one message comfortably.
A typical mirrorless camera RAW file is 25-60 MB. RAWs can't be emailed directly under any normal limit. Either export to JPG first (drops to 5-10 MB at high quality, 1-3 MB at web quality) or share via cloud link.
Screen capture from a 27-inch 5K monitor is roughly 14 MP and 5-15 MB as PNG. Convert to JPG at quality 80 and the same screenshot drops to 800 KB - 1.5 MB without visible loss for content that's mostly photographic. For UI screenshots, PNG with optimisation (optipng or similar) usually compresses better.
PDFs with embedded images sometimes bloat past email limits because each page stores its image at full resolution. Re-exporting the PDF at 150 DPI instead of 300 DPI typically cuts file size by 50-75% with no visible loss for screen viewing.
When attachments aren't the right approach
Sharing photos with non-technical recipients. Drive links work, but some recipients are confused by them or block third-party domains in corporate environments. For older recipients, compressed attachments are often more reliable than any cloud link.
Sending files that need long-term retention. Email attachments are easy to lose track of. For files the recipient might need months later, send a cloud link with a clear filename — they'll find it again, whereas the email gets buried in their archive.
Confidential documents. Email attachments live in mail server logs at both ends and are often outside compliance boundaries. For anything sensitive (medical records, legal documents, financial details), use a secure transfer service with audit logging instead.
Files that need to be viewed by multiple people. Sending a 5 MB attachment to 20 recipients consumes 100 MB of total storage across their inboxes. A single Drive link costs nothing extra and lets you update the file once for everyone.
Tools and alternatives
Built-in OS compression. macOS Preview can re-export JPGs at lower quality (File → Export → JPEG → Quality slider). Windows Photos has 'Resize' under the three-dot menu. Both work but offer less precise control than dedicated tools.
Image editors. Photoshop's Save for Web (legacy) and Export As both let you pick exact quality and target file size. GIMP, Affinity Photo, and Photopea (browser-based) offer similar features for free.
Command-line. ImageMagick's mogrify -quality 70 *.jpg compresses an entire folder in seconds. jpegoptim and mozjpeg's cjpeg push the ceiling further with smarter quantisation tables.
For a no-install path, the freeimgtool compressor and any similar browser-based tool let you process photos without uploading them to a server. The processing happens locally; the file never leaves your device.
Frequently asked questions
What if Gmail still bounces my email?
Total attachment size includes base64 overhead (about 35%). Compress more aggressively or send via Google Drive link.
Lossless option?
Not for email. You need lossy compression to fit attachment limits. JPG quality 80 is the practical lossless equivalent for most viewers.
Does compressing PDFs work too?
Yes. Re-exporting a PDF at lower DPI (150 instead of 300) typically halves the size with no visible loss on screen. Image-heavy PDFs benefit most.
Will compressing strip the metadata?
Yes — re-encoding removes EXIF, GPS, and other embedded data by default. That's usually fine for email; it's actually a privacy bonus.
Can I email RAW files?
Not practically. RAWs are 25-60 MB each and proprietary formats that recipients can't open without specialised software. Export to JPG first.