> curl --proxy "http://proxyuser:proxypassword@psproxyurl.smth.tok.eu.int:8012" --ftp-pasv --proxytunnel ftp://ftpuser:ftppassword@ftp-2-cdn.fileservers.net:21  -v
* About to connect() to proxy psproxyurl.smth.tok.eu.int port 8012 (#0)
*   Trying 123.45.678.10...
* Connected to psproxyurl.smth.tok.eu.int (123.45.678.10) port 8012 (#0)
* Establish HTTP proxy tunnel to ftp-2-cdn.fileservers.net:21
* Proxy auth using Basic with user 'proxyuser'
* Server auth using Basic with user 'ftpuser'
> CONNECT ftp-2-cdn.fileservers.net:21 HTTP/1.1
> Host: ftp-2-cdn.fileservers.net:21
> Proxy-Authorization: Basic giEbbHJ1ePrgABerHmkpms=
> User-Agent: curl/7.29.0
> Proxy-Connection: Keep-Alive
>
< HTTP/1.1 503 Service Unavailable
< Cache-Control: no-cache
< Pragma: no-cache
< Content-Type: text/html; charset=utf-8
< Proxy-Connection: close
< Connection: close
< Content-Length: 786
<
* Received HTTP code 503 from proxy after CONNECT
* Connection #0 to host psproxyurl.smth.tok.eu.int left intact
curl: (56) Received HTTP code 503 from proxy after CONNECT