In brief

Sending a file encrypted

The attachment is too big for the mailbox – and too sensitive for a service that can look inside.

Encrypt the file before it leaves your device, and pay attention to where the key sits. Services like WeTransfer transmit encrypted but can access the file themselves. A link whose key is only in the link and never reaches the provider solves both problems at once: size and confidentiality.

The two questions that matter

Who can open the file? Not “who may”, but “who can”. With most transfer services the file sits on the server in a way that lets the operator open it – for previews, for virus scanning, on demand. That is not malice, it is simply how it is built.

How long does it stay? Seven days, thirty, unlimited on a paid account? And what does “deleted” mean – gone from view or really gone?

What the usual routes achieve

Mail attachment. Often fails on size, usually at 10 to 25 MB. And the attachment stays everywhere afterwards.

Transfer services. Solve size elegantly. They only solve confidentiality if they explicitly encrypt end-to-end – otherwise the provider has access.

Cloud folder with a share link. Convenient, but the file stays and often the link does too. Share links are easily forgotten and still work years later.

Encrypted archive plus any route. Secure if the password comes separately. Cumbersome for the other side, and mail filters dislike encrypted archives.

And with tunnl.

With tunnl. the file is split into chunks in your browser and encrypted chunk by chunk before anything is uploaded. Only encrypted blocks sit on the server. The key is in the link behind the # and never reaches us. After the pickup window the file is removed – without anyone having to remember.

What tunnl. cannot do here: Today the limits are 25 MB per file and 100 MB per account. So tunnl. is not meant for videos and large archives; higher limits for the paid options are planned.

Confidential documents by mail · Compared with WeTransfer and Teams · How encryption works