We've found out that when an auto-reply is set to be sent (aka vacation notice), the notification is sent only when the original message is sent to the account name; and no auto-reply is sent when the original message is sent to an alias.
According to what's written in bug 30548, ZCS remembers the addresses it sends auto-reply to for a week, whether messages have been sent to an account name or an alias.
However, we have default mail settings on our setup, and I could received an auto-reply everytime I sent a message to an account, and it never worked for an alias. I was sending my messages from 1 address to multiple accounts and as many aliases (1 alias per account).
I guess we're doing something wrong, but I can't understand what exactly.
We're running ZCS 5.0.9 on SLES 10 x86_64.