Email & Messaging
Email attachment size limits, explained
Every mail provider draws a line somewhere between 10 and 25 MB - and thanks to encoding overhead, your attachment hits that line earlier than its file size suggests. Here are the real limits and the fastest ways to get under them.
Key takeaways
- Gmail and Yahoo accept up to 25 MB per message, Outlook.com and iCloud Mail stop at 20 MB.
- Corporate mail servers commonly cap messages at 10 MB - always design for the recipient's limit, not yours.
- Attachments are Base64-encoded for transport, which inflates them by roughly a third: an 18 MB file becomes a ~24 MB message.
- Compressing images and PDFs before attaching usually beats splitting the mail or switching to cloud links.
The limits by provider
These are the message size limits of the big consumer providers. They change rarely, but they do change - we check them against the providers' official help pages and update this table when something moves.
| Provider | Limit per message | Bigger files |
|---|---|---|
| Gmail | 25 MB | Google Drive link is offered automatically |
| Outlook.com / Hotmail | 20 MB | OneDrive link |
| Microsoft 365 / Exchange | usually 25 MB, admins can set 1-150 MB | OneDrive / SharePoint |
| iCloud Mail | 20 MB | Mail Drop sends up to 5 GB as a link |
| Yahoo Mail | 25 MB | link services |
| GMX / WEB.DE | 20 MB | cloud attachment |
| Company mail servers | often 10 MB | ask IT - many block executables and archives too |
Why an 18 MB file can break a 25 MB limit
Email was designed for text, so binary attachments are converted to Base64 text for transport. That encoding costs about 33-37% extra size. A quick rule of thumb: multiply your attachment by 1.37 and add the message text - if the result crosses the provider's limit, the mail bounces.
This is why an attachment of 18-19 MB is the practical ceiling for a 25 MB provider, and roughly 14 MB for a 20 MB provider. When a bounce message says the mail was rejected as too large even though the file looked fine, encoding overhead is almost always the reason.
The fastest ways to get under the limit
All four steps work without uploading anything: the FileSizeFix tools compress images, PDFs and videos locally in your browser, so a confidential attachment never travels to a third-party server just to get smaller.
- Compress images first - photos are the most common size driver. Converting to an efficient format and capping the longest side at 1600 px keeps them perfectly readable on any screen and typically saves 70-90%.
- Shrink PDFs before attaching. Scanned contracts and brochures often carry uncompressed page images; a target of 1-2 MB is realistic for most documents.
- For videos, do not attach at all above ~20 MB: either compress to a small MP4 or share a link. Our video guide covers the numbers.
- Bundle many small files into a single ZIP - not primarily for compression, but so the mail carries one clean attachment instead of twenty.
When a link beats an attachment
Above roughly 20 MB, links win. Gmail switches to a Google Drive link automatically, iCloud Mail offers Mail Drop up to 5 GB, and Outlook proposes OneDrive. Links also help when the recipient's server is stricter than yours - the mail itself stays tiny.
The trade-off is control: a link can expire, require sign-in or be blocked by corporate filters, and the file lives on a cloud server. For sensitive documents, a compressed attachment under the limit is often the more private choice.
Frequently asked questions
What is the maximum attachment size for Gmail?
Gmail accepts messages up to 25 MB including encoding overhead, which means attachments of roughly 18-19 MB in practice. For anything larger, Gmail automatically offers a Google Drive link.
Why does my email bounce even though the attachment is under the limit?
Attachments are Base64-encoded for transport, which adds about a third to their size. An attachment close to the limit can push the encoded message over it. The recipient's server may also enforce a lower limit than your provider.
Is it safe to compress a confidential document with an online tool?
Only if the tool processes the file locally. The FileSizeFix compressors run entirely in your browser - the file, its name and its content are not uploaded to a server.
Should I ZIP files before emailing them?
ZIP is great for bundling many files into one attachment. It rarely makes photos, videos or PDFs smaller though, because those formats are already compressed - shrink them individually first, then bundle.