The Mailbox Rule governs when an offer is accepted, therefore forming the contract. The rule states that the offer is accepted as soon as the offeree places their acceptance in the mailbox, so long as it is addressed properly and has sufficient postage. In the modern era, courts have applied the mailbox rule to emails, stating that an offer is accepted once the offeree accepts via email to the correct email address. The mailbox rule is also sometimes referred to as the posting rule.
For more detailed information, see our related Contracts terms: