The parties may fix one duration after another, but their contract is concluded only after the completion of the final term. In the case of bilateral agreements, the tender is effective when it reaches the tenderer. The tenderer may accept them until the tenderer receives the tenderer`s notice of withdrawal. Then an offer is revoked. In accordance with the majority rule, called the “mailbox rule”, acceptance is effective with the shipment if the supplier expressly authorizes this method of acceptance for the use of the bidder, even if the acceptance is lost or destroyed during transport. The refusal of the offer or the withdrawal of the conditional acceptance is effective with access. A late or deficient acceptance shall be considered a counter-offer which does not result in a contract unless the tenderer accepts it. If the offers intersect in the post office, there is no binding contract, because an offer cannot be accepted in the absence of knowledge.. .