Whenever I try to Add another email address you own under accounts in my Google Apps account, I get the following error:
You must send through gmail.com SMTP servers when you send as [email protected]. However, this functionality is not available for your account. Please contact your domain administrator for more information.
I have Super Admin access to the Google Apps (I'm the only user) and I already set Outgoing SMTP Server in the Advanced Gmail Settings but it still doesn't work.