Fix SmtpClientTest.SendAsync_CanBeCanceled_SendAsyncCancel test failure

src/libraries/System.Net.Mail/src/System/Net/Mail/SmtpClient.cs

@@ -558,7 +558,8 @@ Exception ProcessException(Exception e, ref bool canceled, bool forceWrapExcepti
                         // for compatibility reasons, don't wrap these exceptions during sync executions
                         (typeof(TIOAdapter) == typeof(SyncReadWriteAdapter) &&
                             (e is SecurityException || e is AuthenticationException)) ||
-                        e is SmtpException)
+                        e is SmtpException ||
+                        e is OperationCanceledException)
                     {
                         return e;
                     }
@@ -574,7 +575,9 @@ Exception ProcessException(Exception e, ref bool canceled, bool forceWrapExcepti
                 // SendCompleted event should ever be invoked only for asynchronous send completions.
                 if (invokeSendCompleted && !synchronous)
                 {
-                    AsyncCompletedEventArgs eventArgs = new AsyncCompletedEventArgs(exception, canceled, userToken);
+                    // If the operation was canceled, Error should be null
+                    Exception? errorToReport = canceled ? null : exception;
+                    AsyncCompletedEventArgs eventArgs = new AsyncCompletedEventArgs(errorToReport, canceled, userToken);
                     OnSendCompleted(eventArgs);
                 }
             }

src/libraries/System.Net.Mail/tests/Functional/SmtpClientTest.cs

@@ -314,20 +314,19 @@ public async Task SendMailAsync_CanBeCanceled_CancellationToken()
             server.ReceiveMultipleConnections = true;
 
             // The server will introduce some fake latency so that the operation can be canceled before the request completes
-            ManualResetEvent serverMre = new ManualResetEvent(false);
-            server.OnConnected += _ => serverMre.WaitOne();
-
             CancellationTokenSource cts = new CancellationTokenSource();
+
+            server.OnConnected += _ => 
+            {
+                // Cancel the operation during actual server communication
+                cts.Cancel();
+            };
 
             var message = new MailMessage("[email protected]", "[email protected]", "Foo", "Bar");
 
             Task sendTask = Task.Run(() => client.SendMailAsync(message, cts.Token));
 
-            cts.Cancel();
-            await Task.Delay(500);
-            serverMre.Set();
-
-            await Assert.ThrowsAsync<TaskCanceledException>(async () => await sendTask).WaitAsync(TestHelper.PassingTestTimeout);
+            await Assert.ThrowsAnyAsync<OperationCanceledException>(async () => await sendTask).WaitAsync(TestHelper.PassingTestTimeout);
 
             // We should still be able to send mail on the SmtpClient instance
             await Task.Run(() => client.SendMailAsync(message)).WaitAsync(TestHelper.PassingTestTimeout);
@@ -370,7 +369,7 @@ public async Task SendAsync_CanBeCanceled_SendAsyncCancel()
             AsyncCompletedEventArgs e = await tcs.Task.WaitAsync(TestHelper.PassingTestTimeout);
             Assert.True(e.Cancelled, "SendAsync should have been canceled");
             _output.WriteLine(e.Error?.ToString() ?? "No error");
-            Assert.IsType<OperationCanceledException>(e.Error.InnerException);
+            Assert.Null(e.Error);
 
             // We should still be able to send mail on the SmtpClient instance
             await client.SendMailAsync(message).WaitAsync(TestHelper.PassingTestTimeout);