Ok, the email is the problem. Because the email contains the @ which will be chopped by openfire filter.
This issue is already fixed in the latest version of openfire 3.10.0.
Solution 1) you use openfire 3.10.0
Solution 2) username should be not the email. (If you create a new user you have also the possibility to save the email)
Example:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?><user> <username>testuser</username> <password>p4ssword</password> <name>Test User</name> <email>test@localhost.de</email></user>