How to send email from domain of my own computer

Question

A little while ago, my computer got hacked (I think) and someone sent me an email to my gmail account. It was from the email address of one of my own domain names [e-mail] and when it was inspected, my hosting company told me that the email was actually sent from my own computer to my gmail. I have no idea how they did this, but I assume that it means that I can do it as well (if only I know how)

[e-mail]) smtp.mail=[e-mail]

This is the information in the header of the email that I received from my own computer (except that I've removed myname)

Can you tell me how I can send an email from my computer using the info below?

Received: from defout.telus.net (outbound04.telus.net [199.185.220.223])
        by mx.google.com with ESMTP id s6si2186612icv.50.2011.08.25.21.01.30;
        Thu, 25 Aug 2011 21:01:31 -0700 (PDT)
Received-SPF: neutral (google.com: 199.185.220.223 is neither permitted nor denied by best guess record for domain of [e-mail]) client-ip=199.185.220.223;
Authentication-Results: mx.google.com; spf=neutral (google.com: 199.185.220.223 is neither permitted nor denied by best guess record for domain of [e-mail]) smtp.mail=[e-mail]
Received: from edtncm02 ([199.185.220.240])
          by priv-edtnes24.telusplanet.net
          (InterMail vM.8.01.03.00 201-2260-125-20100507) with ESMTP
          id <20110826040130.RGIF29925.priv-edtnes24.telusplanet.net@edtncm02>
          for <[e-mail]>;
          Thu, 25 Aug 2011 22:01:30 -0600
Received: from myname-MacBook-Pro.local ([66.183.19.244])
    by edtncm02 with bizsmtp
    id Qs1S1h0105Fy1L201s1U3B; Thu, 25 Aug 2011 22:01:30 -0600
X-Authority-Analysis: v=1.1 cv=fh8/3ufmgdCAtX9QfKYGMq8jmtyEPWZf9gsaXtoBT04=
 c=1 sm=2 a=Vq8LRqZkKnsA:10 a=rq8sP40Sq3rp59Coqs8A:9 a=wPNLvfGTeEIA:10
 a=SSmOFEACAAAA:8 a=Fb0FxIkzc9yU5OfbpswA:9 a=1TM7i2lP1nUA:10
X-Telus-Outbound-IP: 66.183.19.244
Received: by myname-MacBook-Pro.local (Postfix, from userid 501)
    id C7CB51B4602E; Sun,  1 May 2011 03:58:04 -0400 (EDT)
To: [e-mail]
Subject: Testing HTML Email
MIME-Version: 1.0
Content-Type: multipart/alternative;
 boundary="=_13d3050f9a51ccce5cf656766568e808"
From: [e-mail]
Message-Id: <[e-mail]>

Answer 1

You can send mail from the command line using any smtp enabled CLI client.

I am no mac user but if you google for "command line smtp mac" you will find enough information. See this Link for example.