Mac Postfix - Force from address, prevent from using Mac Username After making the switch from Windows using WAMP and sendmail, to Mac using MAMP Pro and hopefully Postfix I am having issues getting the emails configured correctly. I have fully configured the Postfix Smart Host to use a live email account to send the emails. 

When I check the mail.log

Jul 22 11:29:28 John-MacBook postfix/smtp[544]: C5B2926C91C: to=&lt;info@mysite.co.uk&gt;, relay=mail.mysite.com[212.110.123.123]:25, delay=603, delays=602/0.07/0.13/0.03, dsn=5.7.1, status=bounced (host mail.mysite.com[212.110.123.123] said: 553 5.7.1 &lt;john@mysite.co.uk&gt;: Sender address rejected: not owned by user mail@mysite.co.uk (in reply to RCPT TO command))
Jul 22 11:29:28 John-MacBook postfix/cleanup[550]: 4607426CA90: message-id=&lt;20120722102928.4607426CA90@mailer.mysite.co.uk&gt;
Jul 22 11:29:28 John-MacBook postfix/qmgr[502]: 4607426CA90: from=&lt;&gt;, size=2447, nrcpt=1 (queue active)
Jul 22 11:29:28 John-MacBook postfix/bounce[548]: C5B2926C91C: sender non-delivery notification: 4607426CA90
Jul 22 11:29:28 John-MacBook postfix/qmgr[502]: C5B2926C91C: removed
Jul 22 11:29:28 John-MacBook postfix/smtp[543]: 4607426CA90: to=&lt;john@mysite.co.uk&gt;, relay=mail.mysite.com[212.110.123.123]:25, delay=0.19, delays=0.01/0/0.08/0.09, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as 5E2E8D807E)
Jul 22 11:29:28 John-MacBook postfix/qmgr[502]: 4607426CA90: removed



  status=bounced : Sender address rejected: not owned by user
  mail@mysite.co.uk (in reply to RCPT TO command))


I notice here that "john@mysite.co.uk" doesn't exist, actually "john" is my Mac username. How can I force Postfix to always send email using mail@mysite.com? This is the email address it should be using to send the email which I enter into the MAMP PRO control panel.
The issue was caused because Postfix was sending email using my username from the logged in user. 

I was able to get around this problem following this guide:
Sending Email With Postfix And MAMP Pro