diff --git a/packages/effect/src/internal/mailbox.ts b/packages/effect/src/internal/mailbox.ts
index 4b768213d9..875de46fbc 100644
--- a/packages/effect/src/internal/mailbox.ts
+++ b/packages/effect/src/internal/mailbox.ts
@@ -39,6 +39,16 @@ type MailboxState<A, E> = {
     readonly resume: (_: Effect<Array<A>>) => void
   }>
   readonly awaiters: Set<(_: Effect<void, E>) => void>
+} | {
+  readonly _tag: "Closing"
+  readonly takers: Set<(_: Effect<void, E>) => void>
+  readonly offers: Set<{
+    readonly remaining: Array<A>
+    offset: number
+    readonly resume: (_: Effect<Array<A>>) => void
+  }>
+  readonly awaiters: Set<(_: Effect<void, E>) => void>
+  readonly exit: Exit<void, E>
 } | {
   readonly _tag: "Done"
   readonly exit: Exit<void, E>
@@ -76,7 +86,7 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
     })
   }
   private releaseCapacity(n: number) {
-    if (this.state._tag !== "Open") {
+    if (this.state._tag === "Done") {
       return
     } else if (this.state.offers.size === 0) {
       return
@@ -95,14 +105,17 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
       this.state.offers.delete(entry)
       entry.resume(core.exitSucceed([]))
     }
+    if (this.state._tag === "Closing") {
+      this.finalize(this.state.exit)
+    }
   }
   private awaitTake = core.unsafeAsync<void, E>((resume) => {
-    if (this.state._tag !== "Open") {
+    if (this.state._tag === "Done") {
       return resume(this.state.exit)
     }
     this.state.takers.add(resume)
     return core.sync(() => {
-      if (this.state._tag === "Open") {
+      if (this.state._tag !== "Done") {
         this.state.takers.delete(resume)
       }
     })
@@ -118,7 +131,7 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
   }
   private releaseTaker = () => {
     this.scheduleRunning = false
-    if (this.state._tag !== "Open") {
+    if (this.state._tag === "Done") {
       return
     } else if (this.state.takers.size === 0) {
       return
@@ -194,13 +207,19 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
   unsafeDone(exit: Exit<void, E>): boolean {
     if (this.state._tag !== "Open") {
       return false
+    } else if (this.state.offers.size === 0) {
+      this.finalize(exit)
+      return true
+    }
+    this.state = { ...this.state, _tag: "Closing", exit }
+    return true
+  }
+  private finalize(exit: Exit<void, E>) {
+    if (this.state._tag === "Done") {
+      return
     }
     const openState = this.state
     this.state = { _tag: "Done", exit }
-    for (const entry of openState.offers) {
-      entry.resume(core.exitSucceed(entry.remaining.slice(entry.offset)))
-    }
-    openState.offers.clear()
     for (const taker of openState.takers) {
       taker(exit)
     }
@@ -209,7 +228,6 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
       awaiter(exit)
     }
     openState.awaiters.clear()
-    return true
   }
   done(exit: Exit<void, E>) {
     return core.sync(() => this.unsafeDone(exit))
@@ -261,18 +279,18 @@ class MailboxImpl<A, E> implements Api.Mailbox<A, E> {
     return core.zipRight(this.awaitTake, this.take)
   })
   await: Effect<void, E> = core.unsafeAsync<void, E>((resume) => {
-    if (this.state._tag !== "Open") {
+    if (this.state._tag === "Done") {
       return resume(this.state.exit)
     }
     this.state.awaiters.add(resume)
     return core.sync(() => {
-      if (this.state._tag === "Open") {
+      if (this.state._tag !== "Done") {
         this.state.awaiters.delete(resume)
       }
     })
   })
   unsafeSize(): Option.Option<number> {
-    return this.state._tag === "Open" ? Option.some(MutableList.length(this.messages)) : Option.none()
+    return this.state._tag !== "Done" ? Option.some(MutableList.length(this.messages)) : Option.none()
   }
   size = core.sync(() => this.unsafeSize())
 }
diff --git a/packages/effect/test/Mailbox.test.ts b/packages/effect/test/Mailbox.test.ts
index 4be31dc170..999848e59c 100644
--- a/packages/effect/test/Mailbox.test.ts
+++ b/packages/effect/test/Mailbox.test.ts
@@ -49,17 +49,6 @@ describe("Mailbox", () => {
       assert.isFalse(result[1])
     }))
 
-  it.effect("done completes offers", () =>
-    Effect.gen(function*() {
-      const mailbox = yield* Mailbox.make<number>(2)
-      const fiber = yield* mailbox.offerAll([1, 2, 3, 4]).pipe(
-        Effect.fork
-      )
-      yield* Effect.yieldNow()
-      yield* mailbox.done(Exit.void)
-      assert.deepStrictEqual(yield* fiber.await, Exit.succeed([3, 4]))
-    }))
-
   it.effect("done completes takes", () =>
     Effect.gen(function*() {
       const mailbox = yield* Mailbox.make<number>(2)