I have it set up like that to a tee which is why I'm able to send out emails now, but I have to set the "from" option to my actual email from att.net that I get for having them as my ISP.
If I change the from option to anything else I get a 553 relay denied message.
so this works:
sendmail -f "firstname.lastname@example.org t" email@example.com
and this does not
sendmail -f "any_ol_made_up_email@any_ol_domain.com" firstname.lastname@example.org
AT&T's smtp authentication mechanism seems to be making me send a verified "From" with any relayed mail, regardless of having my username and password sent with the email using postfix's sasl_passwd method.
Am I just doing something really retarded? Shouldn't I be able to relay from any name/email address once I authenticate with them using the sasl_passwd method?