Hello, i am a little bit confused.. I have installed Thunderbird on a machine that has absolutely NO "real" network connection except of a VirtualBox Host-Only-Network Adapter that is used by a virtual machine on which the SOCKS v5 proxy service is running. In order to receive emails i have setup Thunderbird to use that SOCKS v5 proxy WITHOUT the option "When using SOCKS v5, use the proxy for DNS requests". So in my opinion, the machine with no network at all but with Thunderbird running has to resolve the ip adress of the mail server with this proxy configuration, and because that machine has no network it should not be able to access the mail server.. But in fact DNS resolving inside Thunderbird DOES work with the setup i have described.