GMail Sender header problem and using other domains

I've been using GMail for a while now as an SMTP server to send my e-mails from other domains, no matter where I am going. What I realized later is that most of the e-mails I send are getting seen as sent by my account, while I'm actually trying to send them as if they were sent from Well, apparently the whole thing is quite compromised. There's an interesting discussion about that here:, and apparently this is the correct way to do it for Google, so not much hope to get improvement there. Another important point is that it is apparently a problem (in certain circumstances) with Google Apps, as the 'On behalf of' header is sent in the e-mail, indicating the e-mail you would have liked to send it from, instead of putting it in the 'Sender' header. Well, that means I'm back to another SMTP server. I don't want it to show as to my customers.