You can't directly setup email accounts or email forwarding for a Domain Alias within the Helm control panel. However, Domain Aliases inherit everything from the Hosted Domain including email accounts. FTP accounts, DNS records, etc. Thus any mailbox you create for your hosted domain can automatically be used by the domain alias as well. For example if your hosted domain was 123.com and your domain alias was 456.com. You could create a mailbox named "admin@123.com" inside of the Helm control panel. That mailbox "admin@123.com" would automatically be usable as "admin@456.com" or any other domain alias setup on that installation for sending and receiving email, logging in to the mailbox or even remotely connecting to the mailbox through a program such as Outlook.
Basically you just need to create the mailbox for the Hosted Domain in the control panel and then you can automatically use that mailbox with any of your aliased domain names instead of the hosted domain name.
