The official client connects on port 443. Can I do that with Psi?
Port 443 is reserved for the HTTPS protocol – the secure version of HTTP. The official client maintains a permanent connection on port 5222, just like any other Jabber/XMPP client in usual configurations. When 5222 is unavailable, Talk connects on 443. This was previously an undocumented extension but now port 443 can behave like 5223. If you’re behind a firewall or a proxy, you might also want to configure a proxy for that account. Note that you will have to select legacy SSL in the account settings for it to work over port 443.