I want to send mail from my Gmail box (firstname.lastname@example.org) that will appear as sent from my Google Apps address (email@example.com).
While setting up the "send as" address, I'm asked to enter my SMTP server, username and password.
I use smtp.example.com with my Google Apps user and password, and I get the following DNS error:
Authentication failed. Please check your username/password.
[Server response: DNS Error: Address resolution of smtp.example.com. failed: Domain name not found code(0) ]
I have MX records set up on my domain host, and they show on Google Apps admin console.