What Is the Mailbox Rule, and How Does It Apply

Essay

What is the mailbox rule, and how does it apply in the following situation? Explain whether acceptance is effective and a contract is formed.
Day 1: An antique dealer e-mails an offer to sell a highly collectible Art Nouveau glass vase to a collector for $1,500.
Day 2: Collector receives the offer, prints out the e-mail, writes "ACCEPTED, 1 Art Nouveau glass vase for $1,500. Collector," and faxes Dealer the acceptance.
Day 3 (9 a.m.): Dealer's assistant receives Collector's fax, but Dealer is out of the store all morning.
Day 3 (12 p.m.): Realizing he can get much more for the vase at auction, Dealer calls Collector to revoke his offer.
Day 3 (1:30 p.m.): Collector's acceptance fax is delivered to Dealer.