Original sentence: Digital signature and encryption must be applied at message creation time (i.Due to hardware manufacturer's negligence, most devices come without user-controlled encryption or digital signature capabilities.Otherwise any node between the sender and the encryption agent could potentially tamper it.on the same device it has been composed) to avoid potential tampering
Edited sentence: An encryption product may also not be practical when mobile users need to send e-mail from outside the corporate network.First, e-mail must be digitally signed at the point it was created to provide non-repudiation for some legal purposes, otherwise the sender could argue that it was tampered with after it left their computer but before it was encrypted at a gateway.There are a number of reasons why an encryption product may not be suitable in all cases