You’re staring at an MBE question where someone mails an acceptance letter on Monday, but the offeror revokes the offer on Tuesday before the letter arrives. Is there a contract? If you hesitated, you’re not alone—the mailbox rule trips up more bar examinees than almost any other Contracts doctrine. Let’s fix that.
What the Mailbox Rule Actually Says
The mailbox rule (also called the “dispatch rule”) establishes when an acceptance becomes effective in contract formation. Here’s the core principle: acceptance is effective upon dispatch—meaning the moment you drop that acceptance letter in the mailbox, not when the offeror receives it.
This is a huge departure from the general rule for other communications in contract law. Offers, revocations, rejections, and counteroffers all become effective upon receipt. But acceptance? That’s effective the instant it leaves the offeree’s control.
Why does this matter? Because timing determines whether a contract exists. If acceptance is effective Monday when mailed, but revocation doesn’t arrive until Wednesday, you have a binding contract as of Monday. The Tuesday revocation attempt came too late.
The Four Exceptions You Must Memorize
The mailbox rule isn’t absolute. The MBE loves testing the exceptions, so you need these locked down.
Exception 1: The offer stipulates acceptance is effective only upon receipt. The offeror controls the terms of the offer. If the offer explicitly states “acceptance must be received by Friday,” then the mailbox rule doesn’t apply. The acceptance must actually arrive by Friday.
Exception 2: Option contracts. When you’re dealing with an option contract—a promise to keep an offer open supported by consideration—acceptance is effective only upon receipt, not dispatch. This makes sense: the offeree has paid for time to decide, so they bear the risk of the acceptance getting lost in transit.
Exception 3: Rejection sent first, then acceptance sent. If the offeree mails a rejection on Monday, then changes their mind and mails an acceptance on Tuesday, whichever communication arrives first controls. The mailbox rule is displaced because the offeror might have relied on the rejection.
Exception 4: Acceptance sent first, then rejection sent. This one’s trickier. If the offeree mails acceptance on Monday, then sends a rejection on Tuesday that arrives first, the acceptance is still effective under the mailbox rule—unless the offeror detrimentally relies on the rejection before the acceptance arrives. If there’s detrimental reliance, the rejection controls.
How the MBE Tests This
Let’s walk through a typical fact pattern:
On June 1, Owner mails Buyer an offer to sell a vintage car for $15,000, stating “This offer will remain open until June 10.” On June 5, Buyer mails a letter accepting the offer. On June 7, Owner sells the car to someone else and emails Buyer to revoke the offer. Buyer’s acceptance letter arrives on June 8. Is there a contract between Owner and Buyer?
Yes. Buyer’s acceptance was effective on June 5 when mailed. Owner’s revocation on June 7 came after a contract was already formed. The fact that the acceptance didn’t arrive until June 8 is irrelevant under the mailbox rule.
Now change one fact: What if Owner’s offer was an option contract—Buyer had paid $100 for Owner’s promise to hold the offer open until June 10?
No contract. Under Exception 2, option contract acceptances are effective only upon receipt. Since the acceptance didn’t arrive until June 8, and Owner revoked on June 7, the revocation was effective first.
The Rejection-Then-Acceptance Trap
Here’s where students get destroyed:
On March 1, Seller offers to sell Buyer 500 widgets at $10 each. On March 3, Buyer mails a rejection. On March 4, Buyer changes his mind and mails an acceptance. The rejection arrives March 5. The acceptance arrives March 6.
Is there a contract? Yes. The rejection arrived first, so under Exception 3, the first arrival controls. The rejection terminated the offer. When the acceptance arrived on March 6, there was no offer left to accept.
Flip it: Same facts, but the acceptance arrives March 5 and the rejection arrives March 6. Now there IS a contract. The acceptance was effective when dispatched on March 4 under the mailbox rule. The later-arriving rejection is irrelevant.
One more variation: Acceptance mailed March 3, rejection mailed March 4, rejection arrives March 5, acceptance arrives March 6. Seller reads the rejection on March 5 and immediately sells the widgets to someone else. Is there a contract with Buyer?
Technically, yes—the acceptance was effective March 3 when mailed. But under Exception 4, if Seller detrimentally relied on the rejection (by selling to someone else), Buyer may be estopped from enforcing the contract. The MBE will ask whether Buyer can enforce, and the answer depends on whether Seller’s reliance was reasonable and detrimental.
Why “Reasonable Medium” Matters
The mailbox rule only applies if the offeree uses an authorized or reasonable medium of acceptance. If the offer says “reply by email,” and you mail a letter, the mailbox rule doesn’t protect you—your acceptance is effective only when received (if at all).
But if the offer doesn’t specify a method, any reasonable medium works. What’s reasonable? Generally, the same method the offeror used, or a method at least as fast. If the offer came by mail, accepting by mail is reasonable. If the offer came by overnight courier, accepting by regular mail might not be.
The UCC is more flexible. Under UCC Section 2-206, unless the offer unambiguously indicates otherwise, an offer to buy goods may be accepted in any manner and by any medium reasonable under the circumstances. That includes accepting by shipping the goods—performance can constitute acceptance.
Revocation Timing: The Other Half of the Puzzle
Remember: revocations are effective upon receipt, not dispatch. This creates an asymmetry that’s tested constantly.
Offeror mails revocation Monday. Offeree mails acceptance Tuesday. Revocation arrives Wednesday.
Contract formed. The acceptance was effective Tuesday when dispatched. The revocation wasn’t effective until Wednesday when received. Too late.
Offeror emails revocation at 9 AM Tuesday. Offeree mails acceptance at 11 AM Tuesday, before checking email. Offeree reads the revocation at 2 PM.
No contract. The revocation was effective when received—which for email is when it arrives in the inbox, not when it’s read. The 9 AM revocation terminated the offer before the 11 AM acceptance was dispatched.
That last scenario is brutal, but it’s exactly the kind of hyper-technical distinction the MBE exploits.
What to Memorize for Test Day
Boil it down to this:
General rule: Acceptance effective upon dispatch (mailbox rule).
Revocations, rejections, counteroffers: Effective upon receipt.
Four exceptions to mailbox rule:
- Offer requires receipt
- Option contracts
- Rejection sent first
- Acceptance sent first, but offeror detrimentally relies on later-arriving rejection
Reasonable medium required: If offeree uses unauthorized method, acceptance effective only upon receipt.
If you can recall those elements in five seconds, you’ll handle 90% of mailbox rule questions. The other 10% will test whether you can apply the exceptions to weird facts—like acceptance sent by carrier pigeon or telegram. Stay calm and work through the elements.
Bringing It All Together
The mailbox rule isn’t conceptually difficult. It’s a timing rule that favors offerees by making acceptance effective early. But the MBE doesn’t test concepts—it tests your ability to apply rules to facts under pressure. You need to recognize whether you’re dealing with an acceptance (mailbox rule applies) or a revocation (receipt rule applies). You need to spot option contracts instantly. You need to untangle rejection-acceptance sequences without second-guessing yourself.
That requires active recall, not passive review. Reading your outline won’t cut it. You need to see the rule, test yourself on the elements, and drill the exceptions until they’re automatic.
If you want all the contract formation timing rules organized for exactly that kind of active recall practice, FlashTables Contracts covers this in a two-column format that makes the mailbox rule, its exceptions, and the related revocation rules impossible to confuse. It’s structured the way a practicing attorney would actually memorize this material—not buried in paragraph form, but laid out for instant retrieval.
Walk into the exam knowing that when you see “mailed an acceptance,” your brain immediately triggers “effective upon dispatch—unless option contract, rejection sent first, or offer requires receipt.” That’s the difference between guessing and knowing. Lock it down now.