Just use Socket.Connect() for .NETStandard 1.3 and 1.6
Just use Socket.Connect() for .NETStandard 1.3 and 1.6

There's no need to use Task.Run() because continuation
from the Dns.GetHostAddressesAsync() has already left us
in another thread context (probably).

jamie-dainton/MailKit,jstedfast/MailKit