Hacker attack???

Hi,

since a couple of days I receive a lot of registrations on my blog. All “users” have a polish e-mail-address. Juster after the E-Mail of the registration I receive a second mail with following content – does anybody can help and now what this is about:

Hi. This is the qmail-send program at skoll.ispgateway.de.
I’m afraid I wasn’t able to deliver your message to the following addresses.
This is a permanent error; I’ve given up. Sorry it didn’t work out.

[Email redacted]:
Connected to 193.17.41.123 but sender was rejected.
Remote host said: 550 Bad SPF records for [gmx.net:46.252.18.143], see http://spf.pobox.com/

— Below this line is a copy of the message.

Return-Path: [Email redacted]
Received: (qmail 24958 invoked from network); 11 Feb 2013 13:18:20 -0000
Received: from unknown (HELO skoll.ispgateway.de) (127.0.0.1)
by localhost with SMTP; 11 Feb 2013 13:18:20 -0000
Received: (from u355538@localhost)
by skoll.ispgateway.de (8.14.4/8.13.6/Submit) id r1BDIBNK024788;
Mon, 11 Feb 2013 14:18:11 +0100
To: [email protected]
Subject: [kielspratineurope.eu] Dein Benutzername und Passwort
X-DFOptimize: BUFfRE5PRAUZHx8fGRJ1HxweHRgFXU9IWU9DXk9EBV1FWE5aWE9ZWQVdWgdGRU1DRARaQlo=
Date: Mon, 11 Feb 2013 13:18:11 +0000
From: [Email redacted]
Message-ID: <[email protected]>
X-Priority: 3
X-Mailer: PHPMailer 5.2.1 (http://code.google.com/a/apache-extras.org/p/phpmailer/)
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain; charset=”UTF-8″

Benutzername: kabirpanth145699
Passwort: 7H6yNc9YQggJ
http://kielspratineurope.eu/wp-login.php