diff --git a/docs/release-notes/.FSharp.Core/8.0.300.md b/docs/release-notes/.FSharp.Core/8.0.300.md
index f1f8588d65b..be97542e410 100644
--- a/docs/release-notes/.FSharp.Core/8.0.300.md
+++ b/docs/release-notes/.FSharp.Core/8.0.300.md
@@ -2,10 +2,12 @@
 
 * Minor tweaks to inline specifications to support Visibility PR ([PR #15484](https://github.com/dotnet/fsharp/pull/15484), [#PR 16427](https://github.com/dotnet/fsharp/pull/15484)
 * Optimize equality in generic contexts. ([PR #16615](https://github.com/dotnet/fsharp/pull/16615))
+* Add a constructor for `MailboxProcessor` with a flag denoting that an exception will be thrown when `Post` is called after the `MailboxProcessor` has been disposed. ([PR #13036](https://github.com/dotnet/fsharp/pull/13036))
 
 ### Fixed
 
 * Preserve original stack traces in resumable state machines generated code if available. ([PR #16568](https://github.com/dotnet/fsharp/pull/16568))
+* Fix receiving and processing mailbox after Dispose. ([PR #13036](https://github.com/dotnet/fsharp/pull/13036))
 * Enforce AttributeTargets on structs and classes. Also update `RequireQualifiedAccessAttribute` and `AutoOpenAttribute` to use `AttributeTargets.Struct` ([PR #16790](https://github.com/dotnet/fsharp/pull/16790))
 * Enforce AttributeTargets on enums. Also update `RequireQualifiedAccessAttribute` to use `AttributeTargets.Enum` ([PR #16887](https://github.com/dotnet/fsharp/pull/16887))
-* Enforce AttributeTargets on delegates. Also update `ReflectedDefinitionAttribute` to use `AttributeTargets.Delegate` ([PR #16891](https://github.com/dotnet/fsharp/pull/16891))
\ No newline at end of file
+* Enforce AttributeTargets on delegates. Also update `ReflectedDefinitionAttribute` to use `AttributeTargets.Delegate` ([PR #16891](https://github.com/dotnet/fsharp/pull/16891))
diff --git a/src/FSharp.Core/mailbox.fs b/src/FSharp.Core/mailbox.fs
index 699e40153b3..a743afc3f41 100644
--- a/src/FSharp.Core/mailbox.fs
+++ b/src/FSharp.Core/mailbox.fs
@@ -60,7 +60,8 @@ module AsyncHelpers =
 
 [<Sealed>]
 [<AutoSerializable(false)>]
-type Mailbox<'Msg>(cancellationSupported: bool) =
+type Mailbox<'Msg>(cancellationSupported: bool, isThrowExceptionAfterDisposed: bool) =
+    let mutable isDisposed = false
     let mutable inboxStore = null
     let arrivals = Queue<'Msg>()
     let syncRoot = arrivals
@@ -174,9 +175,12 @@ type Mailbox<'Msg>(cancellationSupported: bool) =
 
     member x.Post msg =
         lock syncRoot (fun () ->
-
-            // Add the message to the arrivals queue
-            arrivals.Enqueue msg
+            if isDisposed then
+                if isThrowExceptionAfterDisposed then
+                    raise (ObjectDisposedException(nameof Mailbox))
+            else
+                // Add the message to the arrivals queue
+                arrivals.Enqueue msg
 
             // Cooperatively unblock any waiting reader. If there is no waiting
             // reader we just leave the message in the incoming queue
@@ -331,6 +335,13 @@ type Mailbox<'Msg>(cancellationSupported: bool) =
 
     interface System.IDisposable with
         member _.Dispose() =
+            lock syncRoot (fun () ->
+                if isNotNull inboxStore then
+                    inboxStore.Clear()
+
+                arrivals.Clear()
+                isDisposed <- true)
+
             if isNotNull pulse then
                 (pulse :> IDisposable).Dispose()
 
@@ -347,15 +358,23 @@ type AsyncReplyChannel<'Reply>(replyf: 'Reply -> unit) =
 [<Sealed>]
 [<AutoSerializable(false)>]
 [<CompiledName("FSharpMailboxProcessor`1")>]
-type MailboxProcessor<'Msg>(body, ?cancellationToken) =
+type MailboxProcessor<'Msg>(body, isThrowExceptionAfterDisposed, ?cancellationToken) =
 
     let cancellationSupported = cancellationToken.IsSome
     let cancellationToken = defaultArg cancellationToken Async.DefaultCancellationToken
-    let mailbox = new Mailbox<'Msg>(cancellationSupported)
+
+    let mailbox =
+        new Mailbox<'Msg>(cancellationSupported, isThrowExceptionAfterDisposed)
+
     let mutable defaultTimeout = Threading.Timeout.Infinite
     let mutable started = false
     let errorEvent = new Event<Exception>()
 
+    new(body, ?cancellationToken: CancellationToken) =
+        match cancellationToken with
+        | None -> new MailboxProcessor<'Msg>(body, false)
+        | Some ct -> new MailboxProcessor<'Msg>(body, false, ct)
+
     member _.CurrentQueueLength = mailbox.CurrentQueueLength // nb. unprotected access gives an approximation of the queue length
 
     member _.DefaultTimeout
@@ -506,9 +525,23 @@ type MailboxProcessor<'Msg>(body, ?cancellationToken) =
         mailboxProcessor.Start()
         mailboxProcessor
 
+    static member Start(body, isThrowExceptionAfterDisposed, ?cancellationToken) =
+        let mailboxProcessor =
+            new MailboxProcessor<'Msg>(body, isThrowExceptionAfterDisposed, ?cancellationToken = cancellationToken)
+
+        mailboxProcessor.Start()
+        mailboxProcessor
+
     static member StartImmediate(body, ?cancellationToken) =
         let mailboxProcessor =
             new MailboxProcessor<'Msg>(body, ?cancellationToken = cancellationToken)
 
         mailboxProcessor.StartImmediate()
         mailboxProcessor
+
+    static member StartImmediate(body, isThrowExceptionAfterDisposed, ?cancellationToken) =
+        let mailboxProcessor =
+            new MailboxProcessor<'Msg>(body, isThrowExceptionAfterDisposed, ?cancellationToken = cancellationToken)
+
+        mailboxProcessor.StartImmediate()
+        mailboxProcessor
diff --git a/src/FSharp.Core/mailbox.fsi b/src/FSharp.Core/mailbox.fsi
index ae245d8ace0..740ab77080a 100644
--- a/src/FSharp.Core/mailbox.fsi
+++ b/src/FSharp.Core/mailbox.fsi
@@ -43,6 +43,27 @@ type MailboxProcessor<'Msg> =
     /// <example-tbd></example-tbd>
     new: body: (MailboxProcessor<'Msg> -> Async<unit>) * ?cancellationToken: CancellationToken -> MailboxProcessor<'Msg>
 
+    /// <summary>Creates an agent. The <c>body</c> function is used to generate the asynchronous
+    /// computation executed by the agent. This function is not executed until
+    /// <c>Start</c> is called.</summary>
+    ///
+    /// <param name="body">The function to produce an asynchronous computation that will be executed
+    /// as the read loop for the MailboxProcessor when Start is called.</param>
+    /// <param name="isThrowExceptionAfterDisposed">A flag denoting that an exception will be thrown
+    /// when <see cref="F:Microsoft.FSharp.Control.MailboxProcessor.Post"/> is called
+    /// after <see cref="F:Microsoft.FSharp.Control.MailboxProcessor"/> has been disposed.</param>
+    /// <param name="cancellationToken">An optional cancellation token for the <c>body</c>.
+    /// Defaults to <c>Async.DefaultCancellationToken</c>.</param>
+    ///
+    /// <returns>The created MailboxProcessor.</returns>
+    ///
+    /// <example-tbd></example-tbd>
+    new:
+        body: (MailboxProcessor<'Msg> -> Async<unit>) *
+        isThrowExceptionAfterDisposed: bool *
+        ?cancellationToken: CancellationToken ->
+            MailboxProcessor<'Msg>
+
     /// <summary>Creates and starts an agent. The <c>body</c> function is used to generate the asynchronous
     /// computation executed by the agent.</summary>
     ///
@@ -57,6 +78,26 @@ type MailboxProcessor<'Msg> =
     static member Start:
         body: (MailboxProcessor<'Msg> -> Async<unit>) * ?cancellationToken: CancellationToken -> MailboxProcessor<'Msg>
 
+    /// <summary>Creates and starts an agent. The <c>body</c> function is used to generate the asynchronous
+    /// computation executed by the agent.</summary>
+    ///
+    /// <param name="body">The function to produce an asynchronous computation that will be executed
+    /// as the read loop for the MailboxProcessor when Start is called.</param>
+    /// <param name="isThrowExceptionAfterDisposed">A flag denoting that an exception will be thrown
+    /// when <see cref="F:Microsoft.FSharp.Control.MailboxProcessor.Post"/> is called
+    /// after <see cref="F:Microsoft.FSharp.Control.MailboxProcessor"/> has been disposed.</param>
+    /// <param name="cancellationToken">An optional cancellation token for the <c>body</c>.
+    /// Defaults to <c>Async.DefaultCancellationToken</c>.</param>
+    ///
+    /// <returns>The created MailboxProcessor.</returns>
+    ///
+    /// <example-tbd></example-tbd>
+    static member Start:
+        body: (MailboxProcessor<'Msg> -> Async<unit>) *
+        isThrowExceptionAfterDisposed: bool *
+        ?cancellationToken: CancellationToken ->
+            MailboxProcessor<'Msg>
+
     /// <summary>Creates and starts an agent immediately on the current operating system thread. The <c>body</c>
     /// function is used to generate the asynchronous computation executed by the agent.</summary>
     ///
@@ -71,6 +112,26 @@ type MailboxProcessor<'Msg> =
     static member StartImmediate:
         body: (MailboxProcessor<'Msg> -> Async<unit>) * ?cancellationToken: CancellationToken -> MailboxProcessor<'Msg>
 
+    /// <summary>Creates and starts an agent immediately on the current operating system thread. The <c>body</c>
+    /// function is used to generate the asynchronous computation executed by the agent.</summary>
+    ///
+    /// <param name="body">The function to produce an asynchronous computation that will be executed
+    /// as the read loop for the MailboxProcessor when StartImmediately is called.</param>
+    /// <param name="isThrowExceptionAfterDisposed">A flag denotes will be thrown exception
+    /// when <see cref="F:Microsoft.FSharp.Control.MailboxProcessor.Post"/> is called
+    /// after <see cref="F:Microsoft.FSharp.Control.MailboxProcessor"/> disposed.</param>
+    /// <param name="cancellationToken">An optional cancellation token for the <c>body</c>.
+    /// Defaults to <c>Async.DefaultCancellationToken</c>.</param>
+    ///
+    /// <returns>The created MailboxProcessor.</returns>
+    ///
+    /// <example-tbd></example-tbd>
+    static member StartImmediate:
+        body: (MailboxProcessor<'Msg> -> Async<unit>) *
+        isThrowExceptionAfterDisposed: bool *
+        ?cancellationToken: CancellationToken ->
+            MailboxProcessor<'Msg>
+
     /// <summary>Posts a message to the message queue of the MailboxProcessor, asynchronously.</summary>
     ///
     /// <param name="message">The message to post.</param>
diff --git a/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard20.debug.bsl b/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard20.debug.bsl
index e156eba4598..f50a8c62300 100644
--- a/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard20.debug.bsl
+++ b/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard20.debug.bsl
@@ -671,10 +671,13 @@ Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Contro
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpAsync`1[TReply] PostAndAsyncReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpAsync`1[T] Scan[T](Microsoft.FSharp.Core.FSharpFunc`2[TMsg,Microsoft.FSharp.Core.FSharpOption`1[Microsoft.FSharp.Control.FSharpAsync`1[T]]], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpHandler`1[System.Exception] Error
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] Start(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] Start(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] StartImmediate(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] StartImmediate(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Core.FSharpOption`1[TReply] TryPostAndReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: TReply PostAndReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void .ctor(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void .ctor(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void Dispose()
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void Post(TMsg)
diff --git a/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard20.release.bsl b/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard20.release.bsl
index b4cb84825db..964805cfa2e 100644
--- a/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard20.release.bsl
+++ b/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard20.release.bsl
@@ -671,10 +671,13 @@ Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Contro
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpAsync`1[TReply] PostAndAsyncReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpAsync`1[T] Scan[T](Microsoft.FSharp.Core.FSharpFunc`2[TMsg,Microsoft.FSharp.Core.FSharpOption`1[Microsoft.FSharp.Control.FSharpAsync`1[T]]], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpHandler`1[System.Exception] Error
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] Start(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] Start(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] StartImmediate(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] StartImmediate(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Core.FSharpOption`1[TReply] TryPostAndReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: TReply PostAndReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void .ctor(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void .ctor(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void Dispose()
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void Post(TMsg)
diff --git a/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard21.debug.bsl b/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard21.debug.bsl
index adc21566d87..9efe28bb17c 100644
--- a/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard21.debug.bsl
+++ b/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard21.debug.bsl
@@ -671,10 +671,13 @@ Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Contro
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpAsync`1[TReply] PostAndAsyncReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpAsync`1[T] Scan[T](Microsoft.FSharp.Core.FSharpFunc`2[TMsg,Microsoft.FSharp.Core.FSharpOption`1[Microsoft.FSharp.Control.FSharpAsync`1[T]]], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpHandler`1[System.Exception] Error
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] Start(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] Start(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] StartImmediate(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] StartImmediate(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Core.FSharpOption`1[TReply] TryPostAndReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: TReply PostAndReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void .ctor(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void .ctor(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void Dispose()
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void Post(TMsg)
diff --git a/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard21.release.bsl b/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard21.release.bsl
index eba99c47dec..eefd052ca17 100644
--- a/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard21.release.bsl
+++ b/tests/FSharp.Core.UnitTests/FSharp.Core.SurfaceArea.netstandard21.release.bsl
@@ -671,10 +671,13 @@ Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Contro
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpAsync`1[TReply] PostAndAsyncReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpAsync`1[T] Scan[T](Microsoft.FSharp.Core.FSharpFunc`2[TMsg,Microsoft.FSharp.Core.FSharpOption`1[Microsoft.FSharp.Control.FSharpAsync`1[T]]], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpHandler`1[System.Exception] Error
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] Start(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] Start(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] StartImmediate(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg] StartImmediate(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Microsoft.FSharp.Core.FSharpOption`1[TReply] TryPostAndReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: TReply PostAndReply[TReply](Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpAsyncReplyChannel`1[TReply],TMsg], Microsoft.FSharp.Core.FSharpOption`1[System.Int32])
+Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void .ctor(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Boolean, Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void .ctor(Microsoft.FSharp.Core.FSharpFunc`2[Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg],Microsoft.FSharp.Control.FSharpAsync`1[Microsoft.FSharp.Core.Unit]], Microsoft.FSharp.Core.FSharpOption`1[System.Threading.CancellationToken])
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void Dispose()
 Microsoft.FSharp.Control.FSharpMailboxProcessor`1[TMsg]: Void Post(TMsg)
diff --git a/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/MailboxProcessorType.fs b/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/MailboxProcessorType.fs
index 6325e04c887..8c686a8a213 100644
--- a/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/MailboxProcessorType.fs
+++ b/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/MailboxProcessorType.fs
@@ -6,8 +6,9 @@
 namespace FSharp.Core.UnitTests.Control
 
 open System
-open Xunit
 open System.Threading
+open System.Threading.Tasks
+open Xunit
 
 type Message = 
     | Increment of int 
@@ -311,6 +312,93 @@ type MailboxProcessorType() =
 
             finishedEv.Reset() |> ignore
 
+    [<Fact>]
+    member this.``After dispose is called, mailbox should stop receiving and processing messages``() = task {
+        let mutable isSkip = false
+        let mutable actualSkipMessagesCount = 0
+        let mutable actualMessagesCount = 0
+        let sleepDueTime = 100
+        let expectedMessagesCount = 2
+        use mre = new ManualResetEventSlim(false)
+        let mb =
+            MailboxProcessor.Start(fun b ->
+                let rec loop() =
+                     async {
+                        match! b.Receive() with
+                        | Increment _ ->
+                            if isSkip then
+                                actualSkipMessagesCount <- actualSkipMessagesCount + 1
+                                return! loop()
+                            else
+                                do! Async.Sleep sleepDueTime
+                                if not isSkip then
+                                    actualMessagesCount <- actualMessagesCount + 1
+                                    if actualMessagesCount = expectedMessagesCount then mre.Set()
+                                    do! Async.Sleep sleepDueTime
+                                return! loop()
+                        | _ -> ()
+                    }
+                loop()
+            )
+        let post() = Increment 1 |> mb.Post
+
+        [1..4] |> Seq.iter (fun x -> post())
+        do! task {
+            mre.Wait()
+            isSkip <- true
+            (mb :> IDisposable).Dispose()
+            post()
+        }
+
+        Assert.Equal(expectedMessagesCount, actualMessagesCount)
+        Assert.Equal(0, actualSkipMessagesCount)
+        Assert.Equal(0, mb.CurrentQueueLength)
+    }
+
+    [<Fact>]
+    member this.``After dispose is called, mailbox should stop receiving and processing messages with exception``() = task {
+        let mutable isSkip = false
+        let mutable actualSkipMessagesCount = 0
+        let mutable actualMessagesCount = 0
+        let sleepDueTime = 100
+        let expectedMessagesCount = 2
+        use mre = new ManualResetEventSlim(false)
+        let mb =
+            MailboxProcessor.Start((fun b ->
+                let rec loop() =
+                     async {
+                        match! b.Receive() with
+                        | Increment _ ->
+                            if isSkip then
+                                actualSkipMessagesCount <- actualSkipMessagesCount + 1
+                                return! loop()
+                            else
+                                do! Async.Sleep sleepDueTime
+                                if not isSkip then
+                                    actualMessagesCount <- actualMessagesCount + 1
+                                    if actualMessagesCount = expectedMessagesCount then mre.Set()
+                                    do! Async.Sleep sleepDueTime
+                                return! loop()
+                        | _ -> ()
+                    }
+                loop()),
+                true
+            )
+        let post() = Increment 1 |> mb.Post
+
+        [1..4] |> Seq.iter (fun x -> post())
+        do! task {
+            mre.Wait()
+            isSkip <- true
+            (mb :> IDisposable).Dispose()
+            Assert.Throws<ObjectDisposedException>(fun _ -> post()) |> ignore
+        }
+
+        Assert.Equal(expectedMessagesCount, actualMessagesCount)
+        Assert.Equal(0, actualSkipMessagesCount)
+        Assert.Equal(0, mb.CurrentQueueLength)
+    }
+
     [<Fact>]
     member this.Dispose() =
 
diff --git a/vsintegration/tests/UnitTests/LegacyLanguageService/Tests.LanguageService.Completion.fs b/vsintegration/tests/UnitTests/LegacyLanguageService/Tests.LanguageService.Completion.fs
index a88ce83e903..9cc1ed259d9 100644
--- a/vsintegration/tests/UnitTests/LegacyLanguageService/Tests.LanguageService.Completion.fs
+++ b/vsintegration/tests/UnitTests/LegacyLanguageService/Tests.LanguageService.Completion.fs
@@ -4392,7 +4392,7 @@ let x = query { for bbbb in abbbbc(*D0*) do
         // Get description for Expr.Var
         let (CompletionItem(_, _, _, descrFunc, _)) = completions |> Array.find (fun (CompletionItem(name, _, _, _, _)) -> name = "Start")
         let occurrences = this.CountMethodOccurrences(descrFunc(), "Start")
-        AssertEqualWithMessage(1, occurrences, sprintf "Found wrong number of overloads for 'MailboxProcessor.Start'.  Found %A." completions)
+        AssertEqualWithMessage(2, occurrences, sprintf "Found wrong number of overloads for 'MailboxProcessor.Start'.  Found %A." completions)
        
     [<Test;Category("Repro")>]
     member public this.``WithinMatchClause.Bug1603``() =