Who blocks webmail?
Gmail is a browser-based app, so any proxy should work, regardless if it's a socks or http one. I don't get it why you say it's blocked.
On the other hand, port 25 for mailing is closed by most providers - they do this to avoid spamming through their IPs. But even so, you would still be able to access webmail via a proxy that has closed port 25.
Maybe you got IPs blocked by google, in which case is a matter of IP history and their quality.