If the offer is accepted by mail, the contract is concluded at the time the acceptance was booked.  This rule only applies if the parties publish implicitly or explicitly to consider it as a means of acceptance.  Contracts relating to land, misinterpreted letters and immediate lines of communication are excluded. The relevance of this early nineteenth-century rule in modern conditions, where many faster means of communication are available, has been questioned, but the rule remains a good law for now. The parties are not obliged to agree on any duration of a proposed contract before it can be binding. All essential conditions must be agreed and the agreement must not otherwise be uncertain, vague or ambiguous. The requirement of an objective perspective is important in cases where one party asserts that an offer has not been accepted and attempts to exploit the performance of the other party. Here we can use the test to find out if a reasonable bystander (a “fly on the wall”) would have perceived that the party implicitly accepted the offer out of behavior. An offer may be revoked or withdrawn at any time prior to its acceptance. However, such revocation or withdrawal of the offer must be notified to the addressee, either through the supplier or through another reliable source. A promise or deed of a addressee that indicates that he is willing to attach himself to the conditions contained in an offer. Similarly, the recipient`s confirmation that binds the beneficiary to the conditions of a project.
In addition, a supplier may include, when submitting a bid, the period during which the offer will be available. If the tenderer does not accept the tender within that specified period, the tender shall be deemed to be closed. However, a simple invitation to provide information about the terms of the offer is not a counter-offer and leaves the offer intact.  It may be possible to create a demand in such a way that it contributes to the contractual conditions while sustaining the initial offer. A tenderer may revoke a tender before being accepted, but the revocation must be notified to the tenderer (but not necessarily by the tenderer,). If the offer has been made to the whole world, as in the case of Carlill, the revocation must be in a form similar to that of the offer. However, a tender cannot be revoked if it is grouped into a single option (see also the option contract) or if it is a “fixed offer”, in the event that it is irrevocable for the period indicated by the tenderer. There must always be the offer, the acceptance, the consideration, the intention to create legal intentions and the certainty of the conditions. . . .