It’s a complicated question because eSignature laws change from country to country. However, most legally recognized eSignatures have a few things in common.

First, an electronic signature must be connected to the contract, letter, or document in question. There must be a way, baked into the electronic signature, to tell if the text of the document has been changed in any way after it was signed. From there, the E-Signature service must be able to invalidate any signature written on a document that has been changed after the fact.

The signature must also, in some way, be linked to the person signing it — a name, a symbol, or a mark that uniquely identifies the signer.

Finally, the signatories must be able to retain a key unique to their signature in order to prove that they are the person who actually signed the document.

If all of these conditions are met, there’s a good chance the eSignature is legally binding in most regions.