Known Issues - Google Apps for Administrators

Mail sent to a nickname at an alias domain isn't delivered

At this time, Google Apps email won't deliver mail sent to a nickname at a domain alias. To ensure mail is delivered, make sure to send to either a provisioned user account, or to your primary domain. For example, you can send to user@example.com, nickname@example.com, or user@alias.com, but you can't currently send to nickname@alias.com.

うおー。ちょっと面倒なことになってきた。