There are two types of email addresses in HSPC: Those based on a Linux user, and virtual email addresses. When you configure an email address as username@(multiple domains), this is a Linux user email address. The user name for this email address is "username".
When you configure an email address as username@domainname.com, this is a virtual email address. The user name for this email address is username@domainname.com.
Replace "username" with the actual user name and "domainname.com" with the actual domain name.