Smuxi

If you configured a HTTP or SOCKS proxy for Smuxi and you can't connect to an IRC server that probably means the proxy support disallowes the IRC port. This is often seen when Microsoft ISA is used as proxy server. There is no solution that Smuxi can provide. You can nicely ask your system administator if he can allow the IRC port (6667) for you.

For the reference the error returned by the ISA server looks like this:

HTTP/1.1 502 Proxy Error. The specified Secure Sockets Layer (SSL) port is not allowed. ISA Server is not configured to allow SSL requests from this port. Most Web browsers use port 443 for SSL requests. (12204)