Memory leaks

[sasharyabchun]

Hello.
After reciving 200 000 smtp messages the application occupy 150 000 Mb.
And memory usage is increasing.
There are some problems with memory leaks in the aplication.
Could you help me with it.
I thought of using this smtp server for sending sms, but it can't work on prodaction server with this issue.
Thank you.

[RFlipper]

I think the issue in concurrent dictionary "Connections" in "SmtpServer" class it never removes the connections and GC cannot do this because it thinks they are used.

[RFlipper]

@dere4ka looks like @hanswolff has merged my fix and the issue has been fixed