Email Attachment Size Limits
Every major email provider imposes a maximum attachment size. If your files exceed the limit, the email simply won't send — and you'll get a vague error message. Here are the current limits:
| Provider | Max Attachment Size | Notes |
|---|---|---|
| Gmail | 25 MB | Files over 25 MB are automatically uploaded to Google Drive and shared as a link |
| Outlook / Microsoft 365 | 20 MB | Some enterprise accounts allow up to 150 MB via admin configuration |
| Yahoo Mail | 25 MB | Total size across all attachments in a single email |
| Apple Mail (iCloud) | 20 MB | Mail Drop handles larger files (up to 5 GB) via iCloud links |
| ProtonMail | 25 MB | Encrypted attachments have slightly higher overhead |
These limits apply to the total size of all attachments combined, not per file. And because email uses Base64 encoding for binary attachments, the actual overhead is about 33% — meaning a 25 MB limit effectively allows ~18.75 MB of raw file data.
Why Photos Are Usually Too Large
A single photo from a modern smartphone camera (12–50 MP) weighs between 3 MB and 12 MB as a JPEG. That means attaching just 3–5 photos can exceed Gmail's 25 MB limit. RAW files, screenshots from high-DPI displays, and HEIC files from iPhones make the problem even worse.
How to Reduce Image Size for Email
Step 1: Resize to a Reasonable Dimension
Most email recipients view photos on a laptop or phone screen. A 4000×3000 px photo is overkill when displayed in a 600 px wide email pane. Resizing to 1920 px on the longest side is a good default — it's large enough to look sharp on any screen, but typically cuts file size by 60–75%.
Step 2: Compress with the Right Quality
After resizing, apply lossy compression. For email photos, quality 75–80 strikes a good balance between visual fidelity and file size. The recipient won't notice the difference on a screen.
Step 3: Choose JPEG as the Output Format
JPEG is the safest format for email attachments. Every email client, on every platform, renders JPEG inline. Avoid WebP (some older email clients won't display it) and PNG (file sizes are too large for photos).
Step 4: Strip EXIF Metadata
Photos carry EXIF data: camera model, lens settings, GPS coordinates, timestamps. This data adds 10–100 KB per image and can raise privacy concerns — you may not want to share your exact location. Stripping EXIF is a good practice for email.
Using Deflato's Email Preset
Deflato includes a built-in Email preset that applies all of the above settings in one click:
- Upload your photos to deflato.com — drag and drop up to 50 at once.
- Select the Email preset from the presets dropdown. This automatically sets: JPEG output, quality 80, max dimension 1920 px, EXIF stripping enabled.
- Adjust if needed — If you need even smaller files (e.g., for a 20 MB Outlook limit with many photos), drop quality to 70 or reduce max dimension to 1280 px.
- Download the compressed photos and attach them to your email.
How Much Space Will You Save?
Here's what the Email preset typically achieves:
- iPhone 15 Pro photo (12 MP, 4.5 MB HEIC): → 320 KB JPEG (93% reduction)
- Samsung Galaxy S24 photo (50 MP, 10 MB JPEG): → 450 KB JPEG (95% reduction)
- DSLR photo (24 MP, 8 MB JPEG): → 400 KB JPEG (95% reduction)
- Screenshot (2560×1440, 2 MB PNG): → 250 KB JPEG (87% reduction)
At these sizes, you can comfortably attach 30–50 photos in a single email and stay well under the 25 MB limit.
Alternatives for Very Large Files
If you need to send original, full-resolution photos without compression:
- Google Drive / OneDrive / Dropbox — Upload the files and share a link in the email body.
- WeTransfer — Free for files up to 2 GB.
- Apple Mail Drop — Automatically uploads large attachments to iCloud (up to 5 GB).
But for everyday photo sharing — vacation snapshots, product images, event photos — compressing with Deflato is faster and simpler than uploading to a cloud service.
Conclusion
Email attachment limits haven't grown much in a decade, but camera resolutions have. The fix is straightforward: resize, compress to JPEG at quality 75–80, and strip metadata. Deflato's Email preset handles all of this in one step, so you can send dozens of photos without bouncing off the 25 MB ceiling.