Why email attachment limits exist
Email attachment limits exist because email was designed to carry short messages between servers, not large volumes of data. Providers cap attachments at roughly 25 MB to keep mail servers responsive and storage manageable.
How email actually handles a file
An attachment is not sent as a file. It is encoded into text, embedded in the message, and stored in full in every mailbox that receives it.
That encoding increases the size by roughly a third, which is why a 20 MB file can fail against a 25 MB limit.
A message sent to ten recipients is also stored ten times, so a single large attachment multiplies across the system.
Typical limits
The lowest limit along the path decides. Your provider may allow 25 MB while the recipient gateway rejects anything over 10 MB.
| Provider type | Usual limit |
|---|---|
| Common webmail services | About 25 MB |
| Corporate mail servers | Often 10 to 20 MB |
| Older or restrictive gateways | As little as 5 MB |
| File transfer services | Gigabytes to terabytes |
Why the limits have not grown much
- mail servers would have to store every copy of every attachment
- large messages slow down delivery queues for everyone
- antivirus and spam scanning must process the whole message
- link-based sharing solved the problem more efficiently
What replaced attachments
The standard answer is a download link. The message stays small, the data is stored once, and the recipient downloads only if they need it.
Transfer services are built for exactly this: MyAirBridge handles up to 20 GB per transfer on the free tier, which is roughly eight hundred times a typical email limit.
FAQ
Why is the email attachment limit 25 MB?
Because attachments are encoded into the message and stored in every mailbox involved. Limits keep mail servers responsive and storage manageable.
Why was my attachment rejected even though it was under the limit?
Encoding inflates attachments by about a third, and the recipient server may enforce a lower limit than your own provider.
What should I use instead of attachments?
A download link from a transfer service. The email stays small and the file can be far larger than any attachment limit allows.
Summary
Email limits attachments to around 25 MB because every attachment is encoded, transmitted, scanned, and stored in full for each recipient. Link-based delivery avoids all of that, which is why transfer services measure their limits in gigabytes rather than megabytes.