Creating a group is the easiest way to get your Groove account up and running. Please note if you setup forwarding this way you won't have a backup in Gmail of all your incoming emails.
To get started, login to your Google Apps admin area (http://www.google.com/a/domain.com), and select Groups on the main navigation page.
If you already have a group setup for your email address, simply edit the group. If not, create a new group by clicking the Create a new group button in the top, left corner of the Groups tab.
Your group will look something like the below image. The group name can be whatever you choose, and make sure the email matches the one that forwards to Groove. Set Access Level to Team and check the box to allow anyone on the internet to post a message.
Once you've created your group, paste your Groove forwarding address into the Members field. (You can find this address under your mailbox settings.) Add it as an owner to ensure all incoming emails forward to Groove.
Send a test email to your group email address.
It should arrive in Groove shortly. Once the email arrives, you're all set to receive support requests!