await SmtpClient.SendMailAsync never ends

[BogCZE]

Describe the bug

Hi guys,
We've got problem with SmtpClient.SendMailAsync method. When try to send MailMessage with null or empty Body SendMailAsync never ends or throws exception and thread is stucked.

To Reproduce

Steps to reproduce the behavior:

1. Using this version of ASP.NET Core '2.2.1'
2. Run this code - not full code just the main part (we are using our own smtp server)

 using (var smtpClient = InitSmtpClient(smtpConfig)) {
                    try {
                        var mailMessage = new MailMessage('from', 'To', 'Subject' String.Empty);
                        await smtpClient.SendMailAsync(mailMessage).ConfigureAwait(false);
                        await _emailLogic.MarQueueAsReadAsync(e.Id);
                    }
                    catch (Exception ex) {
                        _logger.LogError(ex, ex.Message);
                    }
                }

3. With these arguments new MailMessage('from', 'To', 'Subject' String.Empty)
4. No error or result application just awaits and awaits

Expected behavior

We tried to set Timeout for SmtpClient but after reading documentation we find out that Timeout is not related to SendMailAsync. We expects at least some kind of exception or timeout to be able to react and skip of sending such email. Now just stuck and nothing happens - we run this code using https://blog.maartenballiauw.be/post/2017/08/01/building-a-scheduled-cache-updater-in-aspnet-core-2.html tutorial (it means our email sender runs repeatedly every minute).
Wesolved this issue by add default message to body when null or empty but I think it would be better when this SenMailAsync will not stuck like this at first place.

Additional context

Add any other context about the problem here.
Include the output of dotnet --info
.NET Core SDKs installed:
2.1.201 [C:\Program Files\dotnet\sdk]
2.1.202 [C:\Program Files\dotnet\sdk]
2.1.300 [C:\Program Files\dotnet\sdk]
2.1.301 [C:\Program Files\dotnet\sdk]
2.1.400 [C:\Program Files\dotnet\sdk]
2.1.402 [C:\Program Files\dotnet\sdk]
2.1.403 [C:\Program Files\dotnet\sdk]
2.1.500 [C:\Program Files\dotnet\sdk]
2.1.502 [C:\Program Files\dotnet\sdk]
2.1.503 [C:\Program Files\dotnet\sdk]
2.1.504 [C:\Program Files\dotnet\sdk]
2.2.102 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]

[muratg]

@BogCZE you may want to move this bug to dotnet/corefx repo. It doesn't appear it's related to ASP.NET Core.

[benaadams]

you may want to move this bug to dotnet/corefx repo.

Link here https://github.com/dotnet/corefx

[Eilon]

This issue was moved to dotnet/corefx#35738