The file should contain the signed termination agreement, the relevant contract version and all attachments. For electronic signatures, preserve the signed version, signature data and the identity of the signatories. Where a representative signs, the authority to represent the party should also be documented.
An email saying “we agree” may explain the negotiations, but it does not always replace an agreed form or a complete settlement. Conversely, a short agreement may be sufficient where it clearly identifies the parties, the contract, the end date and the material financial consequences. That cannot be assessed without the actual communications.
Keep records of receipt, payments, returns and handover as well. In a dispute, it should be possible to identify the first agreed version, later amendments and whether the alleged settlement was performed. Section 915 ABGB may assist with remaining ambiguity, but it is not a substitute for reliable documentation.