Hallo:

you see, it is sometimes difficult to get a response from firewalled users. [Testing firewall] is, as far as i know, this:
You cannot ping a firewall (well, you can, but you will not get a response). If you do not get an *ahem* route error and no ping result either, your client supposes the other person is firewalled. So you 'ask' the firewalled client to send ('push') the file to you. But you will never know if you are heard or not, all you can do is to wait. Sometimes *aaarghhh*, ok.

Joke question: What will happen if both are firewalled? (*nothing* hihi....)

Greetings....