HTTPProxyAddress for SMTPSocket?

I need to use a proxy in a WebApp.

For a normal HTTPSocket, I can use: HTTPSocket.HTTPProxyAddress

But how do I use a ProxyAddress with a SMTPSocket?

SMTP can’t use HTTP proxies, only Socks5 proxies. SMTPSocket does not support Socks5 proxies.
You should try the amazing cURL wrapper: RB-libcURL which has support for SMTP and Socks5.

or use MBS CURL Plugin
http://www.monkeybreadsoftware.de/xojo/plugin-curl.shtml