[exim] Problem with helo command / german gmx provider

Hello List,

i got the following error message when I try to send a message to the
german GMX provider:

  SMTP error from remote mail server after RCPT TO:<any@???>:
    host mx0.gmx.de [213.165.64.100]: 550-5.7.1 {mx072} Sorry, your helo
has been denied.
    550 5.7.1 ( http://portal.gmx.net/serverrules )

Can anyone help? I don't found any "helo configuration".

Thanks
Mirko