500 Firewall Error

Hi there. We're getting a 500 Firewall Error when we send emails to an email account we set up and checked via RoundCube. Here is an example of the bounceback error: From: Microsoft Outlook Sent: Sunday, May 19, 2013 12:53 PM To: Kevin Jardine Subject: Undeliverable: canfit vps8372.inmotionhosting.com rejected your message to the following e-mail addresses: Jacqueline Walters (jacqueline@crossbellfitness.com) (jacqueline@crossbellfitness.com) vps8372.inmotionhosting.com gave this error: Firewall Error A problem occurred during the delivery of this message to this e-mail address. Try sending this message again. If the problem continues, please contact your helpdesk. Diagnostic information for administrators: Generating server: SERVER.domain.local jacqueline@crossbellfitness.com vps8372.inmotionhosting.com #500 Firewall Error ## Original message headers: Received: from SERVER.domain.local ([fe80::39e3:518a:e0b9:f0e4]) by SERVER.domain.local ([fe80::39e3:518a:e0b9:f0e4%10]) with mapi id 14.01.0438.000; Sun, 19 May 2013 12:51:55 -0400 From: Kevin Jardine To: "Jacqueline Walters (jacqueline@crossbellfitness.com)" Subject: canfit Thread-Topic: canfit Thread-Index: Ac5UsTMRa2KFgfDNSOu1X4qFRtxzaA== Date: Sun, 19 May 2013 16:51:54 +0000 Message-ID: <4B636F5BB235164294C2C1CF52D96235010A3DDF@SERVER.domain.local> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [207.239.114.206] Content-Type: multipart/alternative; boundary="_000_4B636F5BB235164294C2C1CF52D96235010A3DDFSERVERdomainloc_" MIME-Version: 1.0