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 @gmail.com, while I'm actually trying to send them as if they were sent from @dokeos.com. Well, apparently the whole thing is quite compromised. There's an interesting discussion about that here: http://www.google.com/support/forum/p/Google+Apps/thread?tid=2f66ff4e186cdc8a&hl=en#all, 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 firstname.lastname@example.org to my customers.
My company - Loa Corporation - can offer you a virtual local SMTP server to overcome this problem. See http://www.loapowertools.com.