Why did my 24 MB file bounce when the limit is 25 MB?

Because attachments travel Base64-encoded, which inflates them by about 33%. Your 24 MB file was roughly 32 MB by the time the server measured it, and the limit applies to that encoded size. For a 25 MB limit, keep the actual file at 18 to 19 MB or less.

What attachment size is safe for any recipient?

About 7 MB. Corporate mail servers commonly cap incoming messages at 10 MB, and after the 33% encoding overhead a 7 MB file lands just under that. If you know both ends are consumer accounts like Gmail, you can go up to 18 or 19 MB.

Does zipping a file get around the Base64 overhead?

No. A zip is still an attachment, so it gets Base64-encoded and inflated like anything else. Zipping helps only if the contents compress well - and PDFs, JPEGs, and videos are already compressed, so they barely shrink. Many corporate filters also quarantine zip attachments, which can make delivery less reliable, not more.

Do FileTinker's compression tools upload my file?

No. The PDF, image, and video compressors all run locally in your browser - the file is processed on your own device and never sent to a server. Even a 200 MB video being compressed for email stays on your machine the entire time.

What happens if I attach an oversized file anyway?

It depends on the provider. Gmail quietly uploads anything over 25 MB to Google Drive and sends a link in its place, which some corporate recipients cannot open. Most other providers either refuse the attachment in the compose window or accept the message and bounce it later - and a bounce from the recipient's server can arrive hours after you thought the email was delivered.

Email Attachment Size Limits in 2026 - and the Base64 Trap That Bounces Files That Looked Small Enough

July 5, 20267 min read

You check the file: 24 MB. You check Gmail's limit: 25 MB. You attach it, hit send, and it bounces anyway. Nothing is broken, and you did not misread the limit. Your file really was 24 MB - it just was not 24 MB by the time it reached the mail server. Email has a quiet packaging step that inflates every attachment by about a third, and almost every published size limit is measured after that step, not before. Once you know the math, the bounces stop being mysterious and the fix becomes a simple number: what your file needs to weigh on disk so it fits on the wire. This guide covers the real limits per provider in 2026, the encoding trap that eats a quarter of your budget, how to get a PDF, image, or video under the bar, and when to stop fighting and send a link instead.

Why a 24 MB file bounces off a 25 MB limit

Email is an old, text-based system: the protocols that move messages between servers carry plain characters, not raw binary data, so every attachment gets converted into text before it travels. The standard conversion is called Base64, and it rewrites every 3 bytes of your file as 4 text characters. That ratio is the whole story - four divided by three is a 33% markup, applied to every attachment, every time, before a single size check happens.

So your 24 MB file becomes roughly 32 MB of encoded text on the wire, and 32 is comfortably over a 25 MB ceiling. The limit was never lying to you; it just measures the message as transmitted, encoding included, and nobody puts that in the compose window.

The practical rule is simple. To know what a file will weigh in transit, multiply its size by 4/3. To know the biggest file you can safely attach, take the advertised limit and multiply by 0.75, then shave a little more for the message body, signature, and headers, which count against the same ceiling. For a 25 MB limit, that means aiming for a file of 18 to 19 MB at most.

The real limits in 2026, provider by provider

Here is where the major providers stand, with the same caveat on each: these are the caps on the encoded message, so your real file budget is about three quarters of every number below.

Gmail: 25 MB for sending on personal accounts, and up to 50 MB for receiving. Attach something bigger and Gmail does not bounce it - it silently uploads the file to Google Drive and sends a link instead, which is convenient until your recipient's organization blocks Drive links.
Outlook.com: commonly cited at 20 MB for regular attachments, though Microsoft's numbers vary by client and have shifted over time - the web version has reported higher caps for locally attached files. Treat 20 MB as the safe planning number.
Microsoft 365 and Exchange at work: defaults are typically in the 25 to 35 MB range, but administrators can and do set them lower. Corporate mail servers enforcing 10 MB are still very common in 2026, and some go as low as 5 MB.
Everyone else: most other consumer providers cluster in the 20 to 25 MB range. If you do not know the recipient's provider, assume the strictest plausible limit rather than the friendliest one.

The limit you cannot see: the recipient's server

Your provider's limit only controls whether the message leaves your outbox. The recipient's server applies its own cap on arrival, and when that cap is smaller than yours, your successfully sent message bounces hours later with a cryptic delivery failure - or worse, disappears into a quarantine queue without telling anyone.

This is the asymmetry that catches people out. Gmail-to-Gmail, you have a generous budget: 25 MB to send, 50 MB to receive. Gmail to a law firm running Exchange with a 10 MB cap, your budget is about 7 MB of actual file - and nothing on your side warns you before you send.

That leads to a two-tier rule of thumb. If you know both ends are consumer accounts, a file of 18 to 19 MB will clear a 25 MB limit. If there is any chance a company mail server is involved, get the file under 7 MB - and if it is something the recipient will forward around internally, smaller still, because every forward carries the attachment through the same checks again.

Getting a PDF under the bar

PDFs are the most common oversized attachment, usually because of scanned pages, and they are also the most fixable. The compress-pdf tool on FileTinker compresses to a target size you pick, with presets running from 100 KB up to 10 MB. Rather than offering a vague quality slider, it searches combinations of render quality and scale until it finds the best-looking version that fits under your number, so you can aim directly at the budget you worked out above: pick 5 MB for a corporate recipient and you are safely inside a 10 MB cap even after Base64 inflation.

It also will not make things worse: if your PDF is already under the target you picked, the tool leaves it alone instead of re-processing it. There is a real trade-off in how heavy PDF compression works, and our dedicated guide to compressing PDFs for email covers it in depth. For the common case - a scanned form or contract that needs to reach an inbox - pick a target comfortably under the recipient's limit and send.

Getting images under the bar

A single photo from a current phone is often 4 to 8 MB, so five attached photos can blow through a corporate cap on their own. The compress-image tool works the same way as the PDF one: you pick a target size - 1 MB, 500 KB, and so on - and it compresses the image down to fit. It keeps JPEGs as JPEG, PNGs as PNG, and WebP as WebP, so nothing about the file changes except its weight, and the recipient opens it exactly as they would the original.

The same no-harm rule applies here too. If an image is already under the target you chose, the tool returns your original untouched and simply tells you it is already optimal. For email, 500 KB to 1 MB per photo is a sweet spot: still crisp on any screen, and ten of them together fit inside even a strict 10 MB corporate limit with room for the message itself.

Getting a video under the bar - and knowing when it will not work

Video is the hardest case, because size is roughly bitrate times length and there is no free lunch. The compress-video tool re-encodes your clip to a target size by working backwards: it takes the size you want, divides by the clip's duration, and encodes at the bitrate that lands there. There is a dedicated email preset that targets about 18 MB - exactly the number that clears a 25 MB provider limit after Base64 inflation, rather than a round number that only looks safe.

The whole thing runs in your browser using the MediaRecorder engine, producing MP4 where your browser supports it and WebM otherwise. Nothing uploads: a 200 MB phone video never leaves your machine during compression, which matters when the clip is of your kids or your colleagues.

Be honest with yourself about the math, though. 18 MB spread over a 30-second clip is a healthy bitrate and will look fine. The same 18 MB spread over a 10-minute recording is a starvation diet, and the result will show it. As a rough guide, a couple of minutes of video into an email-sized file is reasonable; beyond that, you are better served by the next section.

When to give up and send a link

Some files should not be attachments no matter how cleverly you compress them. Long videos, raw photo batches, design files that must stay pixel-perfect, anything over about 100 MB - upload these to Google Drive, OneDrive, Dropbox, or your company's file share and email the link. The message stays tiny and the file keeps its full quality.

Links have their own failure modes, which is why they are the fallback and not the default. They expire, they demand sign-ins your recipient may not have, corporate filters sometimes block or distrust them, and they break the paper trail - a contract attached to an email is preserved with the thread forever, while a linked one can be edited or deleted after the fact. For anything that functions as a record, a compressed attachment beats a link.

So the decision tree is short. Already under the recipient's real budget? Attach it. Compressible to that budget? Compress to a target and attach it. Everything else gets a link, with a one-line note about what it is and how long it will stay up.