I'm using Google Apps Standard.
I created an alias (email@example.com) for my account (firstname.lastname@example.org). When people email me at email@example.com, it correctly arrives at my firstname.lastname@example.org email address.
How can I send mail using this alias address? That is, the email@example.com address should appear as the sender to whomever I email, and my real address (firstname.lastname@example.org) should never be revealed to them.