Repeated email forward failures

Repeated email forward failures

I keep getting emails similar to the following. Each of these messages were sent to non-existent users at my domain. It looks like spam is being sent to random usernames at my domain and being rejected by gmail. I have spam filtering turned on. Is there any other way to prevent this from happening?

The following message could not be forwarded to {my gmail address} for {my domain-name email address}

Technical details of the failure: 
5.7.0 This message was blocked because its content presents a potential
5.7.0 security issue. Please visit
5.7.0   https://support.google.com/mail/answer/6590 to review our message
5.7.0 content and attachment content guidelines. nw8si1065546pab.215 - gsmtp

----- Transcript of session follows -----  

Received:from tcarc-71-033.cnt.entelchile.net (tcarc-71-033.cnt.entelchile.net [164.77.159.42]) by mx.zohomail.com
with SMTP id 1459288107234601.7151222713875; Tue, 29 Mar 2016 14:48:27 -0700 (PDT)
Date:Tue, 29 Mar 2016 18:48:22 -0300
From:Isabella Logan < LoganIsabella56@cnt.entelchile.net>
To:Rivera56 < Rivera56@cheslow.com>
Subject:Bill N-318308
Content-Type:multipart/mixed; boundary="Apple-Mail=_8886307F-D086-05F0-B83B-D121A2AC42E7"

P.S: Please note that your email forwarding will be disabled if there are too many failures.