Does Android use a VPN in background when connecting to Exchange? i use Android 2.3.6 stock. I am new to Android.

At work we have a MS Small Business server, it has Exchange for e-mail.
With my laptop (Thunderbird), i can only connect to IMAP if i have a VPN connection to work.
But my android phone can get my email without a VPN connection. But that is not allowed in our firewall! How can it be?
Now the VPN has the same credentials as the email itself. This is probably the way it always works on MS small business server.

I am guessing that Android is so smart that it tries to make VPN connection with the given email credentials when the connection fails initially.

Is that so?
Android doesn't do that (nor do iOS and others).

IMHO it's not smart to automatically try to do such a thing. It's just a coincidence that your credentials are the same for both those very different things.

Exchange credentials and VPN credentials should really be not the same to begin with (for obvious security reasons).