My question is highly related to this — http://discussions.apple.com/thread.jspa?threadID=1602010&tstart=15 — topic. I have the same exact issue on my server (Xserve G5, running 10.5.8 Server). And it's an old issue, too. Federation works for servers who are hosted on the same domain they're serving, so they can be resolved trough an A record, but does not work with gmail.com, yandex.ru — anything that makes use of xmpp-server.tcp SRV record.
So, instead of jabberd/resolver (xmpp-server.tcp.gmail.com) resolved to 184.108.40.206:5269 (1800 seconds to live)
...I see jabberd/resolver (gmail.com) resolved to [220.127.116.11:5269] (60 seconds to live)+
in my server's log.
Luckily, I have access to a bunch of servers, some of them G5's, some of them — Intels. I've checked it literally tens of times — if it's PowerPC it fails and if it's Intel it resolves perfectly.
So, did anybody manage to set up federation with gmail.com and such on Mac OS X 10.5 Server running on PowerPC server, or is an upgrade the easiest workaround?