Why did my Google Group message fail?

If the Google Group's Permission Setting is set to "allow only Group Members to post" (see below), then messages sent from an alias address on the source account will fail because the alias address is not a member of the source Group.You can either change the Group's Permission Setting to "allow anyone to post" or make sure to send from @source.com (instead of sending from the alias) when you want to communicate to the Group.