From ftm
Q: I keep receiving the notice Message distribution : Authorization denied when i try to post to the FTM list from some of my e-mail addresses.
A: This is because you post from an address that is not subscribed, and only subscribers can post.
Solution: Subscribe with the other address also, and set its receiving mode to "no mail" in the list manager.
Additional pitfall: gmail send uses googlemail.com instead of gmail.com.