I am posting a request like this:
requests.post(URL, headers=HEADERS, cookies=COOKIES, data=DATA, proxies=proxy_list[ip_index], timeout=4)
and getting back the bellow error:
HTTPSConnectionPool(host='www.example.com', port=443): Max retries exceeded with url: /someurl (Caused by SSLError(SSLError(1, '[SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1123)')))
Depending on your proxy settings, the proxy server can be to blame for this. If you have set an https_proxy to an https:// path the proxy server can interfere with the validation process of TLS. Changing this to an http://proxy.address allows the proxy server to open the connection, and then the TLS handshake to occur between host and destination.
It can be useful to try curl -v with similar settings to see what's going on, as the python ssl bindings can misinterpret/obscure errors from the underlying library.
At the root of this, I speculate that a recent update in long-term stable images of distros like Debian has led to a raft of these issues emerging where they were perhaps previously invisible.