title: set sender address in postfix smtp relay
body: <p>I have setup postfix locally on my Linux box, it relays to my gmail account. This works nicely thanks to <a href="http://www.howtoforge.com/postfix_relaying_through_another_mailserver" rel="nofollow">http://www.howtoforge.com/postfix_relaying_through_another_mailserver</a></p>
  
  <p>However I would like to be able to specify the sender address (From:), I could not figure out what I needed to do. Does anyone knows how I can specify any of my (pre)configured valid gmail address ? All I could find is this:
  <a href="http://support.google.com/mail/bin/answer.py?hl=en&amp;answer=22370" rel="nofollow">http://support.google.com/mail/bin/answer.py?hl=en&amp;answer=22370</a></p>
  
  <p>Thanks</p>