How to email a file that's too large to attach

You attach the file, click send, and get a message telling you it exceeds the maximum size. The number in that message is rarely the number you expected, and the reason is worth understanding before you start trying to fix it.

The limit is lower than the number suggests

Most providers advertise a 25MB attachment limit. Gmail, Outlook and Yahoo all cluster around that figure. In practice you get noticeably less, for a reason that has nothing to do with policy.

Email cannot carry raw binary data. Attachments are encoded into plain text using Base64, an encoding that represents every three bytes as four characters. That is a 33% overhead, applied to every attachment, every time.

So a 25MB limit is really about 18MB of actual file. A 20MB video becomes roughly 27MB on the wire and bounces, despite appearing to be comfortably inside the limit.

There is a second trap: the limit that matters is the recipient's, not yours. You can send 25MB from an account that allows it and still have the message rejected because the receiving server caps at 10MB. Corporate mail servers are frequently far stricter than consumer providers, and the bounce message often arrives hours later.

Common limits worth knowing:

Work out what is actually large

Before fixing anything, find out what is taking up the space. It is almost always one of three things.

Photographs. A modern phone produces 3–8MB per image. A dozen holiday photos will exceed any limit, and they are also the easiest thing to shrink dramatically.

Scanned documents. A scan is a photograph of a page. At 600 DPI in colour, a single page can be several megabytes, and a twenty-page scan can be larger than a video.

Video. A minute of phone video at 4K is roughly 350MB. Video is essentially never going through email, and the sections below are mostly about the other two.

The fixes, in the order worth trying

1. Resize images before compressing them

This is the biggest win and the one most people skip. If your photographs will be looked at on a screen rather than printed, they do not need 4000 pixels of width.

Halving both dimensions removes about 75% of the pixels, and file size follows roughly in proportion. A 6MB photo becomes about 1.5MB with no visible difference when viewed at normal size. Twelve photos go from 72MB to 18MB in one step.

Resize to around 1600–2000 pixels on the longest side for anything that will be viewed on screen. Use the image resizer and pick "fit inside a box" so portrait and landscape photos are both handled sensibly without cropping.

2. Then compress

Once the dimensions are right, compression removes more. At around 75% quality most photographs are indistinguishable from the original at normal viewing size while being 60–80% smaller.

Doing both in order matters. Resizing then compressing beats aggressive compression alone by a wide margin, because compression is trying to preserve detail while resizing removes detail you were never going to see. The image compressor also has a target-size mode, which is exactly what you want when you know you need to land under a specific number.

3. Send only the pages that matter

For documents, the question is often not how to make the file smaller but why you are sending all of it.

If a landlord needs two pages of a bank statement, send two pages. If a colleague needs the appendix, send the appendix. This is faster for them, smaller for the mail server, and shares considerably less of your information than sending everything.

Use split PDF to extract the pages you actually need. Page order is respected, so you can also reorder while extracting.

4. Split a large document into parts

When the whole document genuinely has to go, splitting it into several emails works. It is inelegant, and everyone has done it.

Split into chunks that each land comfortably under the limit — remember the 33% encoding overhead when choosing a size. Number the parts clearly in the subject line so the recipient can reassemble them, and tell them how many to expect so they know if one goes missing.

5. Zip it — but know when it helps

Compressing into a ZIP archive is the reflex, and it works well for some file types and does almost nothing for others.

It helps substantially for: text documents, spreadsheets, CSV files, source code, and anything with lots of internal repetition.

It helps barely at all for: JPEG, PNG, WebP, MP3, MP4 and PDFs that are mostly images. These are already compressed, and compressing compressed data yields almost nothing — occasionally the archive is very slightly larger.

So zipping a folder of photographs to email them is largely wasted effort. Resizing them is what actually works. Zipping is still useful for bundling many files into one attachment, which is a convenience rather than a size fix.

6. Use a link instead

For genuinely large files — video, large archives, high-resolution originals — a link is the right answer and everything above is a workaround.

Most providers do this automatically. Gmail offers Google Drive above 25MB, Outlook offers OneDrive. Both send a link rather than the file, and both are simpler than fighting the limit.

Two things to watch. Check the permissions — the default sharing setting sometimes requires the recipient to have an account with that provider, and if they do not, they will receive a link they cannot open and may not tell you. And check the expiry, since some transfer services delete files after a set period, which matters if the recipient is not going to look at it this week.

Choosing between them

The decision is mostly about what the file is.

Photographs: resize, then compress. This solves it almost every time and takes under a minute.

Scanned documents: extract the pages needed, then compress if it is still too large. Scans compress well because they are images.

Text documents and spreadsheets: zip them. This is the case zipping was designed for.

Video: use a link. Do not attempt to email video.

Mixed folders: handle the photographs separately, since they are almost certainly the problem, then zip the rest.

A note on scanned documents

If you scan documents regularly, the settings matter more than any later compression.

Scanning in colour at 600 DPI produces enormous files and is unnecessary for ordinary text documents. 300 DPI in greyscale is legible for anything typed, and often a tenth of the size. Reserve colour and high resolution for photographs, signatures you need to reproduce precisely, and documents where colour carries meaning.

If you have already scanned as images, JPG to PDF will assemble them into a single document — and compressing the images first keeps the result manageable, since the images carry their full weight into the PDF.

What not to do

Do not rename the extension. Changing .mov to .pdf does not change the file size and does not fool anything. It will confuse the recipient and may be quarantined.

Do not repeatedly compress the same image. Each lossy pass discards more detail, and the second pass treats the first pass's artefacts as real detail. Always start from the original.

Do not split video into parts. The parts will not play individually, and reassembling them requires software the recipient probably does not have.

Do not assume it went through. If the file was near the limit, follow up. Bounce messages sometimes arrive hours later and sometimes not at all, particularly with corporate servers that silently discard oversized mail.