Email hacked?

How can I tell if this was sent from our pop3, or if it just spoofed our email address? I received a suspicious looking email, so I clicked on it and chose "Message Options", then "Internet Headers".  Does this tell you whether the email came from us?

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Date: Thu, 18 Aug 2016 08:03:55 +0000
From: GoodRx <no-reply@goodrx.com>
MIME-Version: 1.0
Subject: GoodRx - Your My Rx account is set up!
To: joe@contuso.com
Message-ID: <z6Fo25xKSE6khE_UgRnBsA@ismtpd0012p1las1.sendgrid.net>
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