How to reduce image size for email attachments

Most personal email services cap a message at 20 to 25 MB, and that cap covers every attachment in the message plus the text. Gmail allows 25 MB per message, Outlook.com and Yahoo Mail allow 25 MB, iCloud Mail allows 20 MB, and classic Outlook on the desktop stops at 20 MB for Internet accounts and 10 MB by default for Exchange work accounts. To get a photo under those limits, shrink its pixel dimensions, re-save it as a JPEG at a lower quality, and send anything that still doesn't fit as a cloud link.

Last updated: October 8, 2026

What are the attachment limits of the main email providers?

Each limit below comes from the provider's own help page, checked on October 8, 2026. Providers change these numbers, so the links are worth a second look if you are close to the line.

Sources: Gmail attachment limits, Outlook.com attachment limits, Send large files with Outlook, Yahoo Mail attachment limit, iCloud Mail limits and Mail Drop limits.

Your provider's limit is not the only one. The recipient's server has its own limit, and Apple warns in its Mail Drop article that the recipient's email app "might have a smaller message size limit". If you write to a company address, the 10 MB Exchange default is a safer target than your own provider's 25 MB.

Why does a 25 MB limit fit less than 25 MB of photos?

Email was designed to carry text, so attachments are converted to text before they are sent. The standard way to do this is Base64, defined in RFC 2045: every 3 bytes of the file become 4 characters, and the encoded text is split into lines of no more than 76 characters. MDN summarises the result: a Base64 copy of a file is "roughly a third larger" than the original.

The provider pages above don't say whether they measure the limit before or after encoding. If a limit is applied to the encoded message, 25 MB holds about 18 MB of original files (25 × 3 ÷ 4 = 18.75 MB, a little less once line breaks and headers are added). In practice that means a set of photos that adds up to 22 MB on your disk can still be refused.

SnapCompress recommendation: aim for a total of about two thirds of the published limit. That is roughly 16 MB for a 25 MB service, 13 MB for a 20 MB one, and 6 MB for a 10 MB Exchange mailbox.

How do I get a photo under the limit?

The two settings that matter are pixel dimensions and JPEG quality. Format matters only when the photo isn't a JPEG yet. All three steps below run in your browser on SnapCompress; the image is never uploaded.

1. Convert HEIC photos to JPEG

iPhones save photos as HEIC by default. Not every email client or computer opens HEIC files, so a recipient may see an attachment they cannot preview. Convert them first with HEIC to JPG. If you go straight to Compress with a HEIC file, it is converted to JPEG during compression anyway, and the file name changes to .jpg. The HEIC vs JPEG guide covers when keeping HEIC makes sense.

Screenshots and graphics saved as PNG are a separate case. A photo saved as PNG is usually far larger than it needs to be, because PNG is lossless. Converting it to JPEG with Convert is often the single biggest saving. For a screenshot with small text, PNG may stay sharper; check both. See JPEG vs PNG vs WebP for the trade-offs.

2. Reduce the pixel dimensions

File size follows the number of pixels. A 12-megapixel photo (for example 4032 × 3024) has about 12.2 million pixels. Scaled so its long edge is 2048 px, it becomes 2048 × 1536, about 3.1 million pixels, a quarter of the original. The file shrinks with it, even before you touch the quality setting.

SnapCompress recommendation: a long edge of 2048 px for photos that people will view on a screen. That is enough to fill a laptop display and to zoom in a little on a phone. Use 1600 px if you need to send many photos in one message. Keep the full resolution only if the recipient will print the photo or edit it.

To do this, open Resize, tick "Maintain aspect ratio", and enter 2048 as the width for a landscape photo or as the height for a portrait one; the other side is calculated for you. You can also do it in Compress: turn on "Resize Image" and set both "Max Width" and "Max Height" to 2048. The photo is scaled so its longer side fits within that box, and its proportions are kept.

3. Lower the JPEG quality

JPEG quality controls how much detail the encoder throws away. The Compress tool has a quality slider from 10% to 100%, and it starts at 80%.

SnapCompress recommendation:

• 80% for most photos. Differences from the original are hard to see at normal viewing size.
• 70% if the message is still too large after resizing.
• Avoid going below 60% for photos of people or text. Faces and lettering are where blocky artefacts show first.

How much each quality step saves depends on the photo. A sharp landscape with lots of fine detail compresses less than a soft portrait. Measured sizes at different settings, with the test images and method, are in the results of our compressor benchmark. Read the size Compress reports after each change, and lower the quality one step at a time if you are still over.

4. Check the total before you send

Add up the sizes of all the attachments and compare them with your target from the section above. If you are over, the quickest wins are, in order: resize photos you haven't resized yet, drop the long edge to 1600 px, then lower quality to 70%. If you are still over after that, split the photos across two emails or use a link.

For more on how compression works and the difference between lossy and lossless output, see how to compress images and image resizing best practices.

Can my email app shrink photos for me?

Some can, with less control over the result.

• Classic Outlook for Windows has a "Resize large images when I send this message" option under File, then Info, according to Microsoft's large files article.
• Mail on the Mac inserts images at their actual size by default. When other sizes are available, you can pick one from a pop-up menu on the right side of the message header, as described in the Mail for Mac user guide.

These options are convenient for a quick send. Doing it yourself lets you see the final file size, convert HEIC first, and choose the quality.

When should I send a link instead?

Use a cloud link when shrinking the photo would defeat the purpose of sending it:

• The recipient needs the original, for printing, editing, or archiving.
• You are sending RAW or DNG files, or dozens of photos at once.
• Even after resizing and compression, the total is still over the limit.

Each provider has a built-in route. Gmail adds files over 25 MB as a Google Drive link. Outlook.com lets you attach a OneDrive link, and linked files don't count toward the 25 MB message limit, up to 2 GB per file. Apple Mail's Mail Drop uploads attachments up to 5 GB to iCloud, where they expire after 30 days, and Mail Drop attachments don't count against your iCloud storage. The recipient needs to be online to open a link, and Mail Drop links stop working after those 30 days.

Sources

All pages accessed 2026-10-08.

• Google, Gmail Help: attachment size limits
• Microsoft, Unable to attach files in Outlook.com
• Microsoft, Send large files with Outlook
• Yahoo, Yahoo Help: attachment size limit
• Apple, Mailbox size and message sending limits in iCloud
• Apple, Mail Drop limits
• Apple, Add attachments to emails in Mail on Mac
• IETF, RFC 2045, section 6.8: Base64 Content-Transfer-Encoding
• MDN, Base64 glossary entry