spammer using our domain to send out spams

I received a below email this morning. It seems someone trying to send a spam with our domain name (, but then Google STMP rejected it. I'm concerned if our emails server could be listed as blacklist due to the spammers using our domain to send spams out.
I looked at SMTP log of our server, initially thinking the spam was generated by our email server, but couldn't find below email going out from our email server.
Can someone explain what's going on, wheter our emails server sending out the spam or someone sending out the spam using their server, but putting our domain to the spam header manually? Looking at the mail header transfer history, the spam was generated by our email server initially, but it is not.

Microsoft Mail Internet Headers Version 2.0
Received: from ([]) by with Microsoft SMTPSVC(6.0.3790.4675);
       Mon, 5 Oct 2015 08:31:18 -0400
Received: from mailnull by with local (Exim 4.85)
      id 1Zj4vG-0003ZE-Kg
      for; Mon, 05 Oct 2015 19:31:18 +0700
Auto-Submitted: auto-replied
From: Mail Delivery System <>
Subject: Mail delivery failed: returning message to sender
Message-Id: <>
Date: Mon, 05 Oct 2015 19:31:18 +0700
X-AntiAbuse: This header was added to track abuse, please include it with any abuse report
X-AntiAbuse: Primary Hostname -
X-AntiAbuse: Original Domain -
X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12]
X-AntiAbuse: Sender Address Domain -
X-Get-Message-Sender-Via: none
Return-Path: <>
X-OriginalArrivalTime: 05 Oct 2015 12:31:18.0891 (UTC) FILETIME=[BC4323B0:01D0FF69]


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(es) failed:
    (ultimately generated from
    host []
    SMTP error from remote mail server after end of data:
    552-5.7.0 This message was blocked because its content presents a potential
    552-5.7.0 security issue. Please visit
    552-5.7.0 to review our message
    552 5.7.0 content and attachment content guidelines. x63si12231964ywb.214 - gsmtp

------ This is a copy of the message, including all the headers. ------

Return-path: <>
Received: from [] (port=51041
      by with esmtps (TLSv1:AES128-SHA:128)
      (Exim 4.85)
      (envelope-from <>)
      id 1Zj4uz-0003L8-9u
      for; Mon, 05 Oct 2015 19:31:17 +0700
Received: by with SMTP
 id byRRduB; Mon, 05 Oct 2015 08:34:09 -0400
Received: from ( [])  by with ESMTP id Kb4gdMqn5tr8k1OhS7;  Mon, 05 Oct 2015 08:30:09 -0400
Message-ID: <>
Date: Mon, 05 Oct 2015 08:32:09 -0400
From: "Lacey Bartell" <>
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0
MIME-Version: 1.0
Subject: Yost and Sons Invoice (798559177)
Content-Type: multipart/mixed;

Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit

To our valued customer:

Your weekly staffing service invoice is attached. We appreciate your prompt payment.

Please do not hesitate to contact our office if you have any questions.

To ensure you continue to recieve important email from Penmac Staffing.

Thank you for your continued business!

Yost and Sons
Kids & Beauty

Content-Type: application/zip;
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Will SzymkowskiSenior Solution ArchitectCommented:
I would be checking to make sure your Outgoing send rate is throttled to ensure that your server cannot send out thousands of email a minute. You can set this value to 50-100 per 5 minute or whatever vaule required.

I would also check and see if you had some phishing attemtps because if someone has your username and password they can relay off your Exchange server because they can authenticate.

Another important thing to ensure you have as another level of security is a SPF Record as well. They helps ensure the identity of the IP's/SMTP domains you are sending from.

Use to check if your SMTP domain is blacklisted. Also make sure that your Smart Host Device is also scanning Outgoing mail as well, if it is going through your appliance.

crcsupportAuthor Commented:
I have SPF record and relay is turned off from outside  IP address.
My question was if the above header shows if someone trying to send spams out from their server using our domain or if my server really sent the spam out. As I looked at log, the email was not found in outgoing log.
If the spam was sent from the spammer's mail server pretending us, there's nothing I can do, I guess.
I think the header information above seems fake, the spammer put our domain into the header using some sort of spam software before sending the spam to the recipient.
Rick HobbsRETIREDCommented:
It is pretty obvious you have done your due diligence.  With the SPF record in place and the message not appearing in your Outgoing logs. the message is not coming from you.  To be safe, as was mentioned previously, make sure you have set up throttling and they should quickly forget about attempting to spam from your address because everything is blocked and rejected that they try to send.
Alan HardistyCo-OwnerCommented:
"If the spam was sent from the spammer's mail server pretending us, there's nothing I can do, I guess."

That is 100% correct.  The message is simply an NDR bouncing back to you because the spammer spoofed your domain and as the recipient doesn't exist or the message was rejected, the NDR has come back to the spoofed sender on your server.

As everyone has stated, you have SPF setup, so you've done what you can and beyond that, there is nothing you can do - spammers will do what spammers will do.

Your server won't get blacklisted as a result of a spammer spoofing your domain as the messages aren't coming from your server, so it's not under threat.

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crcsupportAuthor Commented:
Thank you, all. I was worrying about my email server getting listed, now I think it's ok to ignore it.
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