Email virus?

I've gotten several returned emails lately saying that it couldn't be delivered to its recipients. I'm thinking I have a virus, but scans with malwarebytes and Avast have come up clean. I'm going to paste the body of the email below. If anyone has any idea how I can get rid of this, please let me know.

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of
its recipients. This is a permanent error. The following address
failed:

"tristan.krech@gmail.com":
SMTP error from remote server after transfer of mail text:
host: gmail-smtp-in.l.google.com
5.7.0 This message was blocked because its content presents a potential
5.7.0 security issue. Please visit
5.7.0 http://support.google.com/mail/bin/answer.py?answer=6590 to review our
5.7.0 message content and attachment content guidelines. b2si15273864wix.117 - gsmtp


--- The header of the original message is following. ---

Received: from [212.227.15.17] ([212.227.15.17]) by mx-ha.web.de (mxweb003)
 with ESMTP (Nemesis) id 0MFvKI-1YWQuO1ICE-00EsGq for
 <tristan.krech@gmail.com>; Mon, 20 Apr 2015 12:04:23 +0200
Received: from eastrmfepo103.cox.net ([68.230.241.215]) by mx-ha.web.de
 (mxweb003) with ESMTP (Nemesis) id 0LvUgt-1ZSmij1I6l-010dnV for
 <tristan_krech@web.de>; Mon, 20 Apr 2015 12:04:22 +0200
Received: from eastrmimpo305 ([68.230.241.237]) by eastrmfepo103.cox.net
          (InterMail vM.8.01.05.15 201-2260-151-145-20131218) with ESMTP
          id <20150420100421.YBVI32693.eastrmfepo103.cox.net@eastrmimpo305>
          for <tristan_krech@web.de>; Mon, 20 Apr 2015 06:04:21 -0400
Received: from Brigitte ([193.154.21.7])
by eastrmimpo305 with cox
id JA401q00Z09AFfl01A49Dj; Mon, 20 Apr 2015 06:04:20 -0400
X-CT-Class: Virus_Medium
X-CT-Score: 1.00
X-CT-RefID: str=0001.0A020202.5534CF25.00D0,ss=1,re=0.000,vtr=str,vl=1,fgs=0
X-CT-Spam: 0
X-Authority-Analysis: v=2.0 cv=bY61ppzB c=1 sm=1 p=lZENibdfKpnCsjeVwBEA:9
 a=7BIPTak+ZuQ4YhJaOeBVBQ==:17 a=kviXuzpPAAAA:8 a=QEXdDO2ut3YA:10
 a=iRGiX7b12bfk7duQOjUA:9 a=IKIoO-ieCDEA:10 a=Sf_gFPzhefAA:10
 a=vEhjjJ5LO1l4PU-8:21 a=kVH0R7c_deUiTJ-D:21 a=7BIPTak+ZuQ4YhJaOeBVBQ==:117
X-CM-Score: 100.00
Authentication-Results: cox.net; auth=pass (LOGIN)
 smtp.auth=dsteenbock@cox.net
From: "Abrechnung Bank Payment AG" <dsteenbock@cox.net>
To: "Geh_da_weg" <tristan_krech@web.de>
Subject: Rechnung noch offen 20.04.2015 Nr. 18799439
Date: Mon, 20 Apr 2015 10:04:07 GMT
Message-ID: <002eb95d.26198dd35b15eecd@Brigitte>
Mime-Version: 1.0
Content-Type: multipart/mixed;
boundary="----=_NextPart_000_0025_26D029E8.1C0A90BD"
X-UI-Out-Filterresults: notjunk:1;