Your email attachment is too large

What each service allows

Every figure below is linked to the provider's own documentation, because these move. If you are on a work account, your administrator may have set something lower than the default, and their number is the one that counts.

Why a 24 MB file fails a 25 MB limit

Email was designed to carry text, so anything that is not text has to be turned into text before it can travel. That encoding is lossless but not free: the same bytes take up roughly a third more room once encoded. Google says its receiving limits are measured after encoding, "which adds about a 37% increase". Microsoft calls it a 33% translation encoding increase and applies it to any message that leaves its own datacentres.

So the number in the error message is not the number your file manager shows you. Treat a 25 MB limit as about 18 MB of actual file, and a 35 MB limit as about 26 MB, and the problem goes away. Microsoft's own web client does this arithmetic for you and quietly restricts what you can send to 25% below the configured setting.

Getting a real attachment under the line

1. Photos: resize before you compress. A modern phone photo is several thousand pixels across. Set a maximum width of 1600 in resize an image and a dozen holiday photos will drop from tens of megabytes to a few. Then run compress at quality 85 for the rest.
2. iPhone photos: convert them anyway. HEIC attachments can arrive as files some recipients cannot open: Windows needs Microsoft's HEIF and HEVC extensions to view them. HEIC to JPG fixes the size and the compatibility in one pass, and there is a page specifically about HEIC in email.
3. Photographs saved as PNG: change the format. This is a common cause of an absurdly large attachment. PNG to JPG usually removes most of the file in one step.
4. Documents: compress, then split. Compress a PDF first. If a long scan is still over, split it into two or three parts and send them in order.
5. Many attachments: make them one. Mail systems measure the whole message, not each file. Images to PDF turns twenty photos into a single document that compresses far better than twenty separate ones.

Why these limits exist

A mail server does not stream an attachment past; it accepts the whole message, scans it, queues it, and often stores a copy for every recipient. Send a 100 MB file to a team of thirty and a provider has just been asked to write several gigabytes for one click. Limits keep one person's video from delaying everyone else's mail, which is the reason Microsoft gives outright: size limits "prevent large messages from blocking delivery of other messages".

There is a second reason that gets less attention. Mail is copied, forwarded and archived indefinitely, and once an attachment is in that system nobody can call it back. A link can be revoked. That is a real argument for the link route, quite apart from the size.

What the refusal looks like

Classic Outlook for Windows stops you before you send, with wording Microsoft documents exactly: "The file you're attaching is bigger than the server allows. Try putting the file in a shared location and sending a link instead." On a POP or IMAP account that appears at 20 MB of attachments; on an older on-premises Exchange Server mailbox Microsoft's article gives a 10 MB default, set by the administrator rather than the app (Microsoft 365 mailboxes default to 35 MB).

Gmail does not refuse at all. It removes the attachment, uploads it to your Drive and leaves a link in the message, and checks whether your recipients can open it, asking you to change the sharing if they cannot. Mailing lists and work accounts can still leave someone without access, so check before you assume it arrived.

A server further along the chain can also reject a message you have already sent, which comes back as a bounce, sometimes much later. If that is what happened, the recipient's limit was the smaller one.

When it still will not fit

• Send the link. A far higher ceiling, revocable, and one copy instead of thirty.
• Cut dimensions, not quality. Going from 1600 pixels wide to 1200 is invisible in an email and usually saves more than dropping a JPG to a low quality setting, which you can see.
• Split the document. Two emails with half a report each will always beat one that bounces.
• Send what they need, not what you have. A scanned signature page is one page. An insurer wants a legible photograph of the damage, not a 48 megapixel original.
• Check the file is not secretly an image dump. A presentation exported to PDF with full-resolution photos in it is mostly photograph. Compress the images and rebuild it with images to PDF.

If it was not the size

• The message named a format: file type not supported.
• It was a web form rather than an email: file too large to upload.
• Something else entirely: why was my file rejected.
• Worth knowing before you hand a payslip to a stranger's server to compress: why none of this needs an upload.

Frequently asked questions