... don't seem to like each other any more. If you happen to have the same problem, then the same fix that has been discussed under the Kopete bug report works here as well:

Exchange

jabber.gmx.net

against

xmpp-gmx.gmx.net

in Account settings -> Advanced -> Connect server

The reason seems to be a too sloppy implementation of the XMPP RFC (concerning hostname resolution) in the libpurple implementation.