Gmail's new feature
As a Gmail user I've sometimes trouble with certain email alias unhappy of me sending from an SMTP server outside of our campus network. Another source of weirdness is the fact that while the From: field shows what I want, there is also a, sometimes not hidden, "On behalf of" that is broadcasting my gmail account even when I'm not interested on doing so.
It's great that Gmail has added a new feature that allows Gmail servers to use your organization SMTP server as the outgoing SMTP server for your corporate email address.
The two above mentioned problems are fixed then: You can send to email alias only intended for local users just right from Gmail (no nasty Outlook anymore, thanks). And secondly, there is only now the right From: mailbox.