Some very popular german (and of course international) free mail services support their „own“ messengersystem which is based on the Jabber/XMMP protocol. So, with the right information, you should be able to use them with any jabber-messengerclient.
Konfiguration
Every GMX-Mailaddress is functional Jabber-Account
Username: <yourmail@address>
Password: <yourmailpassword>
Jabberserver: jabber.gmx.net
Options:
SSL (port 5223), plaintext-password
After first supporting only the addresses connected to 1&1 domains (online.de, onlinehome.de), now it is possible to use every mailaccount with your own domain name.
Username: <yourmail@address>
Password: <yourmailpassword>
Jabberserver: jabber.1und1.de
Options:
SSL (port 5223), plaintext-password
Username: <yourmail@address>
Password: <yourmailpassword>
Jabberserver: jabber.gmx.net
Options:
SSL (port 5223), plaintext-password
Username: <yourmail@address>
Password: <yourmailpassword>
Jabberserver: talk.google.com
Options:
SSL (port 5223), plaintext-password