Download the application (http://psi-im.org/) and install it as usual. Then click on “Account Setup”.

Click on “Add”.

Chose an alias for your account and check the box “Register new account”.

Enter “macjabber.com” as the server you want to register with. Check the box “Manually Specify Server Host” and enter “macjabber.de” as the host. Then click on “Next”.

Click on”Trust this Domain” or “Connect anyway” when this notice shows. (The server has a certificate in the name of “macjabber.de” – not “macjabber.com – which you selected as your connecting server in the previous step.)

Chose a username and password for your account ‘@macjabber.com’ and click “Next”. If the name is already in use, a failure notices pops up. Just try again with a different name.

Next up will be this notice, if you registered successfully:

Your account details will be shown in a new window. Click on “Save” and the setup is finished.