This stops us depending on properly-configured SRV records.
'fallback-servers' is not good enough in this situation:
• foo.com's XMPP stuff is served by Google Apps;
• your router breaks SRV requests;
• foo.com resolves to 1.2.3.4 which has a (different) XMPP server
listening on port 5222.
This may seem far-fetched, but this happened to two completely different
people, both hosted with Dreamhost.