ConnectionManager check for idle connections is incorrect

[mzboray]

We are running Papercut as a service. Once in a while we are seeing a failed send on the smtp client side when disposing our SmtpClient instance with the error:

System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags)
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
--- End of inner exception stack trace ---
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset, Int32 size)
at System.Net.Mail.SmtpPooledStream.Dispose(Boolean disposing)
at System.IO.Stream.Close()
at System.Net.ConnectionPool.Destroy(PooledStream pooledStream)
at System.Net.ConnectionPool.ForceCleanup()
at System.Net.ConnectionPoolManager.CleanupConnectionPool(ServicePoint servicePoint, String groupName)

The papercut log seems to indicate a connection was closed for being idle, but i'm not sure how we could have had it open for any great length of time:

2017-05-15 13:35:19.024 -07:00 [Information] Session timeout, disconnecting 32556

Looking at the logic, I believe the comparison check for idle connections in ConnectionManager is incorrect

// Loop through the connections
foreach (int key in keys)
{
	// If they have been idle for too long, disconnect them
	if (DateTime.Now < _connections[key].LastActivity.AddMinutes(20))
	{
		Logger.Information(
			"Session timeout, disconnecting {ConnectionId}",
			_connections[key].Id);
		_connections[key].Close();
	}
}

The comparison should be DateTime.Now > _connections[key].LastActivity.AddMinutes(20), i.e. close the connection if the current time is more than 20 minutes after the last activity. I can submit a pull request later on.

[mzboray]

Fixed by #53.