How it is proven that an e-mail or text message (SMS) was not forged by the recipient?
<p><a href="https://law.stackexchange.com/questions/16763">Here</a>, it was said that a text message is legally binding. But I am interesting in that what would happen when the sender says that the message was not sent by them. It is not a challenging problem to get any „forged“ text message (or e-mail) to the device. Will the court request an information about the message from the service provider? Do mobile operators even store the text of the messages (in the EU)? What would happen when the operator would not able to provide the information?</p>
<p>Imagine this situation:</p>
<ol>
<li><p>I sell something. The sender wants to buy that.</p>
</li>
<li><p>I receive a text message (using SMS), sent to me using a mobile network operator. Let's say that it says that the sender wants to buy that 100 €. I aggree.</p>
</li>
<li><p>I modify the text of the message in the device (without changing the length, sender information, timestamps, character encoding etc.). Now, the message says that the sender must pay 200 €.</p>
</li>
<li><p>The sender receives the thing, pays 100 €. I use the message as a evidence of that the sender agreed to pay 200 €. The sender also tries to use the (original) message stored in sender's device as an evidence for that the price was 100 €.</p>
</li>
</ol>
<p>How can it be proven (e.g. at the court) that one of the messages was actually sent by the sender? I can imagine that the mobile network operator would provide an information about the message, but what if the text was not stored by the operator?</p>

<h2>Each side presents the evidence that they wish and the court decides who to believe</h2>
<p>This will involve lay witnesses who testify to what they saw and heard, expert witnesses who can give opinions and physical evidence.</p>
<p>The onus of proof lies on the plaintiff, the one seeking the extra money, so they have to prove their version. If the court gives more weight to their version, they win. If the give less weight or equal weight, they lose.</p>

contract-law european-union digital-contract binding texting