I'm sending from foo@domain.com. That's not a real address, it's an alias that delivers to bar@domain.com.
The bounces I'm getting seem to be saying the problem is that foo@domain.com doesn't exist. If that's as designed, in other words of the receiving system should reject anything sent from an alias, then I need to not use an alias.
Is that what the bounce messages are saying?
If it matters, it's not an explicit alias. I have *@domain.com delivered to the main inbox.